Hi Pete,
Ooops
my misreading of your post,
Usually the six spring centre nuts are not tight ?? theres always a first time though
In the photos you can see my home made locking tool,
Phil Pearson the Goldie Guru makes a sliding plate with a bush and seal,
But, I think these are designed to work with his own clutch ?? Not sure on this?
There are several ways to improve the sealing on the sliding plate,
I have made a few different versions which are a definite improvement on the original
SRM sell a felt ring that fits between the adaptor and sliding plate ??
An improved oil resistant foam seal can replace the big felt, ( which always leaked profusely on mine)
http://www.ebay.co.uk/itm/BSA-GOLD-STAR-B31-B33-A7-A10-PRIMARY-CHAIN-CASE-IMPROVED-SEAL-42-7504-/172034761152?hash=item280e1221c0:g:wj8AAOxyYANTYklWI saw a post somewhere pointing out a very possible leak path between the two parts of the sliding plate
a run of sealer around the joint will help a bit there
A "perfect" seal at the sliding plate will then require a case breather
HTH
John