have a compression and a cylinder leakdown test done on the engine. it's not likely, but possible, the block and rings are worn bad enough to allow the boost from the turbo get past the rings and slightly pressurizing the crankcase. i've seen it on 2 85 b230fts, never a late 1. i think volvo hardened the blocks in the later b230s. the 2 i refer to were out by .060 and .080 in the bore. the first one we saw, we hung 3 turbos on it before i realized the problem. 3rd new turbo, oil smoke out the exhaust. removed the oil cap and the dipstick and the smoke cleared up. not gone, but much less. pulled the head and there was a fat lip at the top of the bore like i've never seen on a volvo 4. i've put stock rings in blocks, like 1 of mine, that had 250k miles on them. used motors fixed it. again, you may be right. more often than not, it's the turbo. but i'd hate to see you hang a turbo when it needs a motor to fix the problem. good luck, chuck.