How often to demagnetize mc cartridges?

Never.

All the best.

JD

Dear @wcheng2 : I still have the same Sumiko you own. I used several years ago and in those old times I thought it makes that the cartridge recovery its " transparency " or something like that.
I used till the fluxbusting damaged one of my cartridges, I can't remember which one, burn-in one of the coil wire and I always followed the Sumiko precise instructions.

In those times I did too with MM taking the cantilever/stylus out.

So it's hard to say if it's safe to do it with LOMC cartridges and if with today designs really makes a recovery " up-date " in the cartridge performance. Maybe I will test it with some of my LOMC cartridges. We will see.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

I don’t seriously disagree with those who say never to use a flux buster like the Sumiko. As I mentioned, I only and occasionally use the Cardas test LP for that purpose, and it does seem to rejuvenate MC cartridges. My rationale is that I am fairly sure that playing an LP is not going to damage the magnet in the cartridge. It is probably a very gentle process, if it actually does any good at all. But one cannot say often enough, never demagnetize an MM cartridge. The same probably holds for an MI type, although maybe less dangerous in that case. In fact, I once owned an Aesthetix Janus preamplifier which has a demagnetization circuit that you can switch in. I was so leery of accidentally damaging any of my precious vintage MM cartridges that I disabled that circuit.

Never done it.  No need. 

Did get the manual but it doesn't mention or recommend time between treatments.  

Thanks for your responses everyone!  I think I'll just try using the fluxbuster every few weeks or so.