I don't recall any mast bumping problems but then I haven't flown it since 1970. I do remember the Bendix (?) coupling had a bad reputation. The pilot who relieved me two days later flew into the top of Mt Otto in PNG and all 3 on board died. The Bendix coupling was broken but I never heard if it broke before or after the tragic accident.
I remember the autos were much more hairy than in a Bell 206 or 47!!