I have been a busy boy today. I reassembled the primary drive using the used clutch crown that I bought from a BSAOC member. The replacement clutch, along with new rollers has less slack than the one I had before.
Musky, I took the chain tensioner off to decide if I wanted to modify it and attach a piece of nylon chopping board the way you have. The rubbing area of the tensioner is hardened. I pondered sharpening a masonary bit to drill it but decided that my time is too short to muck about and possibly bugger the job up. Maybe another time!
I found some tiny fibre washers to put under the heads of the case screws. I think the oil leaked out, ( causing the damage) from the designated drain screw, that has a hole in the screw boss inside the case. So today, I got carried away and fitted fibre washers to all of the screws.
You can see my other updates from today in other forum headings.