If your ordering on line, I'd go with the Heavy Shockproof, it's sightly cheaper, my local dealer charged me a dollar more and I've always had good luck with it, really makes the trans shifts smooth! But either would work, I get mine locally and so I'll just get which ever they carry. As for the MTL, I used it, but think that the fluid used in the primary isn't as important as the motor, or trans. As I've said in the past, the main job of this fluid is heat transfer. But some fluids can be a problem with the clutch, so you don't want to use just anything. I think MTL, is overkill, but again, I've been using it. Now have the primary case oil because that's what the local shop carries!
V-Twin Primary Case Oil
Red Line’s new V-twin Primary Case Oil is designed specifically for ’84-to-present V-Twin American motorcycle engines, including aftermarket engines of similar designs. Similar to our MTL, this product is for use in the primary chaincase with wet-diaphragm spring clutches.
Designed to operate over a wide temperature range, this Primary Case Oil improves clutch operation while reducing wear and temperature. Where most synthetics are too slippery for clutch operation, this friction-balanced product is balanced to provide less slip, smoother operation, and helps to apply more power in modified engines.
Craig