I also use Dex and Sport+ 4, I buy it by the case from Kitfox.
As to checking oil level I pull it though a few times and check the level, if it is close to the bottom of the acceptable range I know I am good. I do a full "burp" once in a while to confirm (usually near the top of the range). I got this advise from Ken Lockwood.
Dorsal ~~^~~
Series 7 - Tri-Gear
912 ULS Warp Drive