Lectro88 your fear is well placed. Mineral oil has a lot of paraffin wax in its make up. In older machines that have run dino oil for their whole life, the seals will wear, as they wear the paraffin in the oil replaces the seal. If you switch to a PAO (synthetic) it will clean the paraffin and start leaking like a sieve. Also with new engines your supposed to wait until 10k miles before changing to a PAO so the rings will seat. The PAO can hinder the engine break in because of the superior protection, does this make sense? There are many benefits to running PAO oils but there are applications that its not. I dont pay for lubricants because I work for a lubricant manufacturer (yes I am one of the dreaded sales guys) and I use dino oils in my pre 1980 machines.