Someone was asking about sight glasses for the oil level somewhere in this web site but buggered if I can find it now
Anyhow
What I did was to get an ordinary oil seal the correct diameter and cut the lips out of it , leaving just the outer ( rubber coated steel ) ring . I then pestered the local glassier ( window shop ) to cut me a small 4mm thick piece of glass to fit inside the ring which I siliconed into place and for the reflector , I used an english 1/2 crown coin with 2 small holes drilled top and bottom . The glass guy didnt even charge me as he is into bikes too ( actually a harley but thats close ,I geuss ) ha ha

It was me who was trying to find a sight glass. I haven't been able to find the time to work on my Paso since September, but I like what you wound up doing. It will be interesting to see how well it holds up to the bike's vibration and heat cycles.

just to let you know , the sight glass is holding up well, 7000 k's , 2 oil changes