There was a temporary issue with the Series 3000 single shaft dual mags (mainly) whereby TCM stopped making the mags and while most parts were available under PMA, not all of them were, which resulted in a temporary parts shortage for
overhauls.
Under FAA Part 91, there is normally a 500hr
inspection, not an overhaul, and that dealt with it in the meantime.
When I heard of the impending demise of the mag parts, I quickly bought a whole factory overhauled mag ($2.5k) so I have a spare on the shelf, which is damn useful.
Recently, during the parts shortage, the mag came up for an overhaul, and the key part (an impulse coupling spring) was listed at a certain well known UK EASA145 firm near Oxford. So I sent them the mag for an overhaul. Afterwards they refused to let me have a copy of the work pack... I complained to the CAA who were totally (suprisingly actively, I thought) disinterested. Obviously I wasn't going to fly with this suspect mag, so despite having just paid £800 for the OH I sent it to the USA to be re-done (by then the parts were available). It's back on the shelf now
I prefer to overhaul my mag at 500hrs because the casing is then NDTd, which is important because a cracked housing near the mounting bracket can cause it to come off the engine...