I didn't use any on my Lo Boy and it's held up OK with just the gasket.
My new favorite sealant is 'Hylomar'. It's non-hardening and supposed to be reusable. Will give it a good test on the engine when I finally get the tranny back together. But the oil pan and front cover have held ok so far. It is a bit hard to locate, but packaged by Permatex. Ebay or Amazon is the easiest.
1971 Cub (Rufus) 1950 Cub (Cathy) 1965 Lo Boy Fast Hitch (Nameless III) 1970 Cub 1000 Loader & Fast Hitch (Lee)