I would NEVER use RTV to seal a set of cases. That is not what it is designed for.
I would use threebond 1104:
Case Sealant Liquid Gasket TB1104
A synthetic rubber, that is a semi-drying, visco-elastic sealer which is resistant to oil, water, gasoline, and chemicals. Application areas include sealing transmission case covers, motorcycle cases, timing chain cases, side covers, 2-piece cylinders, clutch housing bolts and oil filter mounting
Or permatex Anerobic flange sealer:
Permatex