These things dont have a head gasket as such nnnnnorman, just a few O rings to seal the oil and water holes and the base gasket , if there at all is just a steel shim. There are gaskets under the engine covers but these are best replaced with 3 bond or similar . My 906 had a gasket between the crankcase halves which must be replaced if disturbed however I was told after splitting the cases that the gasket was NLA and to just use 3 bond , which would have required the re shimming of the 3 shafts ( bulk hassle ) so I bought a sheet of .9mm gasket paper and cut my own ( I F2 glue one crankcase gasket face and with the gasket paper laid of a FLAT surface place the crankcase on the paper and stack on a few weights until glue is properly dry and then trim off excess with a razor blade and a dremel sanding wheel ), so you'd wanna be sure that you had a good reason to split the cases . I split mine ( if Im gunna be honest ) coz I was bored , but I did want to check the top gear gear set as I had been told this was often the first real sign of wear ( apparently they get noticably noisey although I think its more a case of not realising how bad it was till it was fixed ). Gearbox out put berring can take a beating if the chain has been run to tight but that would surprise me going by your comments re the chain hitting the swing arm . Mine also has big chain gouges in the swingarm caused by running the chain to loose and not replacing the chain guide. Sinse I have owned the bike and kept the chain tight and fitted a new guide there has been no problems. One thing for sure nnnnnnorman ,if you split the cases you would be mad not to replace all the berrings and seals you can. Yours is not what I would call a "high miler " ( mine has 78,000 kms ) especially if it has had a good service regime, but once your in there ...... One reason I pulled my paso down was that I found it a noisey motor , and some noises came and went , so I thought I'd have a wee look up its arse
