This is what is happening. This is the very condensed version.

Dino oil has an ingredient, totally unintentional, that swells seals a bit. It comes in the crude oil and is not one of the many additives that are in all engine oils.

Synthetic oils do not have this naturally occuring ingredient in sufficient quantity. But due to the incidents of syn oils leaking, the oil companies are adding a component to help with this. Also the auto mfgrs are switching to seal materials that will work well with syn oils.

I switched years ago and had a few leaks that went away in a month or two. Do some research on your syn brands to find out which are addressing the problem.

__________________
Frank
540/6

Dirrezas (4) @ 275/35-18, Eibach springs & bars, Bilstein Sports, Dinan Stage 2, slotted ATEs, Hi-Temp HTP pads, SS Lines, UUC-SS, White/Tan, Bling-free & Stealthy