JB Weld or Hi Temp RTV silicone oil crack fix.

The Franklin engine I rebuilt came with an odd ball cast aluminum oil
pan with a big shaft access hole in back. May have been a helicopter
engine oil pan. I put a disc there and welded it shut (from outside).
But the weld is dripping some oil especially when hot. I
am planing to take out the oil pan and fill the inside groove between
the disc and oil pan with either JB weld or Hi Temp RTV silicone.
The RTV works great as gasket to seal out other holes with plates
bolted on them. But there would be no pressure plate to hold it in the
groove in this case. Which one is better choice? Another sealer?

I don't want to get another oil pan since I adapted this shape
for other uses.

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SQ2000 canard: http://www.abri.com/sq2000