Thanx for the info. I think it's glued in. I have the appropriate pliers and it won't budge. I have another one that came right out no problem.I have an older style MD2 and 4 that have serial numbers, my old Hound dog head has a serial number also.
My recent MD4 doesn't have a serial number, so I don't think he's using serial numbers anymore?
As far as it being matched to the head goes, I don't think so. My Hound dog/MD4 came as a pair with different numbers so the numbers are only associated with the individual components and I doubt a data base was kept on what sold with what.
As far as the hi/low ring goes, it's glued in place on heads like the hound dog etc, but if it's just an M61 then it should be able to be removed.
The previous owner may have used thread lock? It's not necessary but who knows?
I don't use anything special to remove the rings, just some appropriately sized needle nosed pliers. There's specific pliers that might do a better job. I'm thinking something like circlip pliers might work better on a stubborn ring?