Recently bought a pair of SV cylinders, the “mechanic” that installed them used a lot of silicone to be sure they where “leakproof” DONT DO THIS !! Needles to say that they have to be overhauled to maybe the 3th size. (because of the oil starvation, rather deep scrathes)
Assuming (Assume Nothing!), Start again, Assuming mating surfaces are as near to 100% perfect as possible, i.e. cylinder to crankcase, or cylinder (barrel) to cylinder head, NEVER use silicone. Obtain or make the best gasket possible. For paper gaskets, Corn Flakes packets are good. Great care must be taken to make sure oilways are not obstructed or blocked!
In the early days the most common gasket sealant was grease applied thinly to all mating surfaces and to both sides of the gasket. I found a good product called GASKET-GOO, impervious to oil, steam, etc., yet the joint could be taken apart without trouble.
A note for Dnepr OHV 650cc with copper cylinder head gaskets, these should be “annealed” (heating to cherry-red, no quenching required) before fitment, applying GASKET-GOO or similar product. You DON’T want something that just sets like CEMENT!