Decided to keep the original clutch cover ( probs have to anyway) but I would like to at the very least remove and clean the clutch slave piston or replace piston, is there a trick of the trade to remove this

As clutch seemed to work ok when I got the bike maybe I don't have to touch the slave piston at all?

Id clean the thing out at the least, you may be surprized how much shit there is in there and it doesn't flush out when you fill er up with fresh fluid . There is a mod ( p750 tech section I think ) about fitting the later clutch piston with a couple of roller skate bearings and a brass(?) mushroom . Its a good mod.

It seems the slave unit is available at steinedinse, problem is how to remove the old, is it a matter of drilling it out or is there a simple tested way , cheers

The cover is already off , tried compressed air down the intake tube with no luck , she's popped out maybe 2 mm just enough to get fingernails to it but won't move, tried croc soak to try help , now triedfreeze and release , tried a tap with a soft mallet, I might try to rig an old brake leavers to it but sounds like a pain, can I just pull the green seal out first

Compressed air should work unless the piston is really seized. Be sure the bleed nipple is closed and maybe wrap something around the tip of the air blow gun so you don`t lose so much pressure. You`ll also notice that the correct angle matters. I know the problem from removing brake caliper pistons. It will take a while to move very little. Push it back in a bit and repeat a few times. After a few attempts it should come out.
Removing the seal won`t do much. I wouldn`t attempt trying to pull the piston out by using pliers unless you don`t care if it survives.

Will try again tonight left soaking in crc, don't think it's seized as she would spin with my finger before the 2 mm out situ , don't want to use force at this stage as it appears all good, thanks

Yeah that's a bitch not coming out with air , have to try hook up a master cylinder or try to pull it out, if I pull out will I guess pull the seal first, I haven't seen replacement cost yet but will do soon, pretty sure I have spare master somewhere so that's the next attempt , I won't be happy just leaving it

A master cylinder should work once the system is bled.
Pulling it out can't be an option. You can only grab it by the center pin once the seal is out but the pin is only held in place by a thin circlip. As stuck as the piston seems to be when pulling on it the circlip will probably give and you`ll hold the pin in one hand, the clutch cover in the other with the piston still in it and numerous bearing balls will be rolling over the floor somewhere.
If you ruin it Stein Dinse sells the piston for €142.50. The one of the Monster/ST4/748 etc is €39.50 + a bearing and pin which you`ll probably have to have machined somewhere.

With time and if the clutch isn`t used the rubber O-ring will stick to the cylinder. If the clutch is then operated it can tear the O-ring causing a leak. You may find rubber sticking in the cylinder bore once the piston is out. The O-ring can be replaced with the modern V-type seal (#93040091A).
Also if the brake fluid isn`t replaced on regular basis the absorbed water in it can cause a piston to rust.
For assembly I meanwile use ATE brake master cylinder grease (ATE 03990205012). Not (!) to be mistaken with the brake caliper lubricant that is applied on the back of brake pads or on brake caliper pins. The master cylinder grease is a special grease which other than caliper grease is used on pistons and rubber seals and which does not react with brake fluid.

data sheet:
https://app.box.com/s/ognks2mehubw6261825r0wr0ent04my7

Thanks a lot for that I will get my head around all that and see how it goes on the weekend,this bike likes to throwlots of challenges just gotta keep pluggin away

Well i have a brembo frt bke lever / master off 850 lemans to or. ig clutch line to housing to bleed bottle all on a downward trend fixed by vice/ tape/ etc I hate dealing with brake fluid but anyhow I can't even get it to flown down to clutch cover, pumping lever to bleed brakes to what I know with no luck

The clutch is generally more difficult to bleed (maybe due to the design of the clutch cover). Are you sure the master cylinder is ok?
If you have a large syringe and a thin rubber hose you can try to fill in the brake fluid by the bleed screw of the clutch cover until it gets to the master cylinder or you can improvise.
In the past I've used an undercoat gun to bleed brakes or the clutch if it didn`t work the 'normal' way. Not a subtle or really recommended way to do it but it worked for me. I attached a hose to the bottom tube and via a reducing piece a thinner hose that would fit on the bleed nipple. Pull the trigger then open the bleed screw. One needs to be sensible when operating this setup otherwise brake fluid will be sprayed all over. Also it should not be done in the garage or with a car standing nearby. At least not if you`ve never done it this way before

The clutch can be a bitch to bleed , and pushing the fluid up from the bleed nipple back up the line to the master cyl ( crack the banjo at the master cyl as there is always a bubble hiding in there )is the easiest way. I think its the internal diameter that makes it hard to bleed normally . The large dia makes it easy for the bubbles to rise back up the line faster than you can pump them down. As G sez the master cylinder must be good . If the rear seal ( the outer most one ) leaks as you release the lever and the piston returns to battery rather than only drawing fluid from the resivior it will also draw in air past the seal. This is a hideous situation because the clutch may well have been working fine while full of fluid , its not until you try to bleed a "dry" system that the seal causes issues ........... and this can lead one to believe the master cylinder is in good order and dismiss this as the problem.............and continue

I have replaced lemans reservoir with new 89 unit and bleed the system of air bubbles, not sure of the degree of resistance on lever as not accustomed to this bikes clutch action , the thing is it's not having any effect on the slave pin / piston , not sure where to go from here, I think I need to look at pulling the thing out , any more help is much appreciated