I have a Merc.150 EFI, can i use any lower end lube or should I stay with with what Merc. promote's? I was going to go get some at a Gander store and just thought I better ask?

Stay with Manufacture recommendations. Don't want to blow a lower unit to save a few bucks, plus if anything goes out at least you know you used the right oil. Just my two cents.

I use penzoil but depending on the year of your motor you may want to stay with the recommended brand. Especially if there is still a warranty clause

as long as you use a product that meets manufacturers specs they have to honor your warranty. otherwise there would be no aftermarket products on the market for anything and we would all have to pay up the wazoo for everything we own. the Sierra semi synthetic is probably one of the best gear oils out there pricewise and quality wise. we go through about 100 gals a year at our shop and have never had a problem.