The two internal drain studs next to the oversized sleeves are where most of the oil was leaking from initially. It got thin in that area from boring for the sleeves. Couldnt get the exopy in place to cure the problem. There are now Teflon seals/orings around all studs on top of the block. I also use silicone sealant under the drain studs seals. Yeah, silicone, curse words to a real mechanic.
As to the RC block, I don't think it has cooling fins like the stock cylinder so no passage is there for leakage with the large sleeves.