We were changing angle drive fluid up here once a year on our own Slings (and a few others), or every other year on all the rest. Now that we've got 85w-250 we're probably going to switch to every other year. It's cheap and easy enough to do. And the plugs are 8mm allen, not Torx. And yes, do not over tighten them, a gentle snug is all you need.
85w 250 huh? How's it working out? What brand you using?