Are we talking about the now quite famous El Camino, with 367K on the clock? I am voting for your vigilant cleaning efforts with ARX. How many totally loaded filters from cleaning and rinses were there? Is that oil pressure guage a mechanical one in the 1983 unit? Is may be some of the tubing was clogged, or even if it is an electrical one the sending unit may have been severely coated with gunk.
My guess is that you are getting oil change intervals with heavily clogged filters at this time, after the many cleaning and rinses. I have always been a YB and PP fan. But to be honest have never experienced any earth startling cleaning from either, on their own. I do think that PP is a great oil to run the maintenance dose in however. Unless changed, the PP is a group III oil, which allows to be labeled synthetic. In essence is is an ultra refined dino basically. Of coarse there are the adaptive molecules that can mend the oils viscocity characteristics if it gets sheared. And yes there is a marketing campaign that is ongoing that Pennzoil products clean up 46% of sludge compared to something, or what they used to do, in the first oil change.
But honestly you must ask yourself, if PP could have cleaned out all the sludge in your motor with simple oil changes? I can't see it. Auto-Rx recommends PP or other group III's for cleaning and rinsing for those that feel that they must run a synthetic in their motors. A bit pricey for my taste, for a couple short OCI's, cleaning and rinse. Is it any more effect cleaning and rinse to run a group III versus running a group II dino? My vote is no.
If you want to go to extended drains in a clean or cleaned up motor, then a group III with the maintenance dose is hard to beat.
