Here is my $0.02
I have been using the Pennzoil Premium Plus for 3 years now and have had 0 problems. In fact, I had my mercury mechanic check it out during the last service and he doesn't see any difference in those engines vs ones that use the Mercury brand. I buy it at Academy in the 2.5 gallon jugs for about $6-7 per gallon. I had one other mechanic tell me I NEEDED to use ONLY the Mercury brand. When I asked him how is their refining specs on TCW Premium Plus oils any different, he didn't know. If I recall correctly, Mercury doesn't own refineries so they must be buying it from someone else anyway. Just an opinion and definitely saves $$$$.