Myself i would use the Merc premium gear lube..Its the good stuff.
Everyone has different opinions on oil...As long as it is GL-5 rated gear lube it will work.
Merc Hi Performance is the good stuff (it's green to blue green in color). There is also a Merc PREMIUM gear lube (looks the same color as oil).
They are NOT the same.
New Merc outdrives and most lower units on outboards are filled with PREMIUM gear lube for breakin. After that, the recommended it Hi Performance gear lube.
I have no problems using the Hi Performance gear lube in my Volvo DP (When I had it) and have no problem recommending it for use with Merc, OMC Cobra drives, Volvo DP and all SX/DP-S drives. (Not Volvo single prop drives 93 and earlier.)
OK, I know that Merc Hi Performance and Premium are different and can't be mixed. My question, if you're draining one and refilling with the other is there any flushing of the old (besides draining it) that needs to take place?
And what if you were to mix High Performance and Premium Gear Lube Oil? Also, where can you get the washer that goes with the drain screw that fits into the lower unit? Oops, mine happened to fall into the old gear lube and was hoping to just pick one up (cheap) at west marine or bass if they readily carried them.