From the block area as 2wd the oil is cooler, not having picked up as much heat on it's way through the engine, there is also less potential for foreign bodies, ie carbon deposits to get in the line, as it touches less engine surface, all the crap that collects in the normal running of a engine carbon wise seems to find it's way to the oil galleries in the head, and lodge at the rear of the channels, where on the exhaust side it is further baked into submission from the hot exhaust!!
tabetha