I had a 165 at one time, you might toe it in just a touch and see if that stops the problem if the fluid doesn't. It really doesn't matter much what you use as long as it ALL you use. You can drain/flush and just use 20 wt hydro oil but it is better not to mix ATF and Hydro.
A couple of the bigger construction outfits here use NOTHING but 10X40 oil in EVERYTHING. They use it in hyraulics, PS, engine crankcases and auto trannies on heavy equipment. They feel that it is better than having someone add the wrong stuff...
