What's a real good arm for a Decca Cartridge?

Thanks for all the info! I've got a test record on the way and I'll add even more mass to my Fidelity Research headshell. I've been lining the inside of the headshell with the lead tape that is normally used for golf and tennis equipment. That has allowed me to use the extra balancing weight of the M2-12R. I've been noticing since I posted originally that the mistracking happens almost always at the same place, about 2/3 into an LP. I wonder if I have to readdress my alignment?

If your alignment is *close* to correct it is likely not the culprit. How much does your 'dressed' headshell weigh now?

I would guess around 26g.

Here's a weird one. I swapped out the 3" maple shelf I had installed on my wall shelf just a month ago and went back to the 1/2" maple shelf I was using before and it has only misracked once since then in two days of listening. Either the rigidness of the thicker shelf was bad or somehow there was something wrong about how the table was sitting on the thicker shelf, even though I checked and rechecked the leveling. 

Hmm. Higher self resonance frequency for the thinner shelf? Interesting indeed.

A word about Trans-Fi linear tracker.
 All my higher quality cartridges, both very low compliant and very high compliant can do all the Telarc 1812 Overture cannons because the Trans-Fi  arm is capable. But only a couple of them can do the very last cannons with an authority that leaves me speechless. Trans-Fi T3Pro is able to distinguish true tracking ability with ease and obviously the true very finest cartridges. I don´t have a Decca Jubilee not to mention the Reference but my friend also runs a T3Pro and hasn´t had issues with his Jubilee. Trans-Fi linear tracker does the job.