Last resort is try drill and tap 4-6 holes and screw a plate on with that liquid metal stuff below the plate? It may work, may not?
+1 Good idea from streido...
I think it would really work when done properly, I would even try a liquid sealant like Curil instead of epoxy - it's guaranteed to be oil-proof and heat resistant enough for this application, and also cheaper and easier to work with...
Take care not to leave some large aluminium chips from drilling in the crankcase. Use a sharp drill bit and drill very slowly so the bit produces one continuous chip of aluminium instead of loose crumbs. Also try to stop at the exact moment the drill is coming through at the other side of the material... With a bit of luck (no pun intended
) you can get away with this without disassembling the cylinder etc. Drain and filter the oil afterwards, and repeat this after letting the engine idle for a short wile, just to make sure there's nothing left in there...
Update : It might even work when you use liquid sealant or epoxy to just glue an aluminium plate over the hole, without drilling and tapping for screws, it depends on the surface area that's available though... Also make sure that your crankcase ventilation isn't blocked, so there's no pressure buildup..