Quote Originally Posted by neuroanatomist View Post
That's what I'd do, as well. But I'd suggest Loctite Blue because if it doesn't work you'll want to be able to remove it!

If that doesn't work... I use RRS replacement feet on my EF 600/4 II and RF 100-300/2.8, they made one for the EF 100-400 II but it's gone from their website (more broadly, their product selection has shrunk considerably in the last few years). The RRS foot is still available at B&H/Adorama, but it's $30 more than the Kirk foot. OTOH, if you're not opposed to used then KEH has the RRS foot for $68, and since it's a chunk of machined aluminum there's really not much that can go wrong. FWIW, for my R8 I bought the RRS L-bracket for the EOS RP (which fits perfectly) used from KEH and it was in perfect condition (unlike the foot for the 100-400 II, the RP bracket is not available new anywhere I could find).

Good luck!
Thank you both for the suggestion. I'll give the loctite blue a shot before moving on from the Canon foot. I have bought many things from KEH and have been pleased, so no issue doing that for me. I appreciate the help!