Anyone experience this and can advise...

[EVguru]

A mix of Acetone and ATF is one of the best penetrants, although boiling water is quite good. Rust is water soluble.

The hotter you can get the nuts without overheating anything else the better, so a very hot concentrated flame like an OxyAcetlene torch would be good. Papier Mache' can be used to keep things cool and there are commercial products that are even better. A can of freezer spray is a good idea to 'shock' a rust seal loose. The ideal would be to get the stud very cold and the nut very hot to maximise the differential expansion, but you don't really have the access.

When it comes down to it, the studs can be replaced and used/new drums are available. I recall that a new clutch drum is about £60 and makes getting a silky smooth clutch much more likely compared to an old burred up one.