A tube of Loctite 515 Master Gasket for all the gearbox joints.
I find usually I get no leaks at all with this stuff.. and it stays that way. I've got 3 Minis here and none leak...
must go for the Guinness record I guess!
Only downside- it's $20 approx for a tube but it goes a long way.
Buy it at bearing places, they are cheaper than the usual clip joints.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
