Everyone seems to have an opinion on this. My Continental A65 manual does not specify any form of sealant, gasket or thread between the case halves. A film from the 1940s detailing the overhaul of one of these does show the application of some kind of unspecified sealant. Is there a better, modern alternative to using something like "Perfect Seal" and silk thread? (Silk thread is $60 a roll!) Since the manual does not mention thread I'm afraid it might end up creating more bearing clearance. Supposedly it mashes down to nothing, but something has to be thicker than nothing, right? I am leaning to some modern non-hardening sealant, but no idea which yet. And no, I did not at any stage think about squirting some RV stuff in there.