Mobil Av 1 was taken off the general aviation market due to its problem with constant speed propellers.
Somehow it gummed things up.  Surge and rpm stability, if I remember...
At the time I was maintaining a fleet of C-172's (among others) and one engine went over three-thousand hours on Mobil Av 1.  (I finally said: 'no more'!)  We were duly impressed to find NO MEASURABLE CYLINDER WEAR! Pacific Aviation was flying twelve thousand hours a month at that time in the 90's.  Busy, yes.  Happy with Mobil Av 1--- to be sure we were very happy!
Oh, another Lyc O-320 H2AD went 2900 hrs. before an exhaust valve went south.  We flew the C-172 N's exclusively because that motor has no gear reduction assembly.  Many folks hate this engine but it is one of the best. I can overhaul one in my sleep...  And I love the dual mag.  Let's Simonize our watches, Andy.
WPD 90Y