I use AC 0w40 fuill synthetic since the day I got mine. I usually change the oil in them every year before hunting season along with the diff. fluid. I only had a problem with low oil 1 time and it was my fault for not putting the drain plug in all the way

. Glad I didn't use it, it just sat in the garage and dripped oil, luckily I checked it before I went out.
I also use FRAM oil filters, PH6018. I get them at Wal-Mart a lot cheaper than the AC ones, only thing is they are a little shorter than the AC branded ones.