You can run an MTF in a toploader, to speed them up and reduce drag, Valvoline dura gear 75/80 GL4 will be fine, it's thin like auto fuild. In the 80's I used to run M21 holden boxes on auto fuild to speed them up but this offers no extreame pressure protection like diff oil. GL4 oils do. I just use the Dura gear beacuse I use that in my Discovery, it seems to work best in it. It does wear out though, I find in the Disco the syncro performance drops off, change the oil and it's like new again. The MTF oils have additives to make syncro work, diff oils don't. Penrite will make an equivlent, I did try it years ago, but the Disco did not shift as well with it. Dad uses it in his Diesel Disco though.