The simplest solution here is to just get some virgin Merc lube tested.

See if it's any good.

There may even be some posted analysis for the merc oil floating around the net.

out of curiosity how many hours did you have on your drive and did you see flakes in the oil or have a failure

if i remember correctly you are around 750 hp

Ron, I had a failure Im no drive expert but Doug is, he's not sure my it failed possible prop strike ? I dont run my stuff hard just cruising along about 65 and boom, tore the steel tower out of the housing and even broke the shift cable.

Doug K from ROTO?
I told him I`m not running that watery mercury junk and he was fine with it .

Make no difference unless you are running a huge engine on a heavy boat. Any heavy oil will do.