There is overemphasis on CLA's. Mine go in for a service when something is acting up that affects the picture taking. If not - I keep using them until something does!
In the 60's I used M's for press work. underpaid and overworked, CLA's were few and far between. It was often cheaper to pick up another body, than to have an existing body fixed. A lot of shooters were switching to Nikon SLR's and sold of their M's cheap (bl.p M4's $80, bl.p M2 from $60 and M3's were about the same). I used to pitch 'dead" bodies in a box and in mid-80's I dragged these cameras from Sweden in "bundles" of 5 and had them fixed and traded them or sold them. In direct $ it looked good, but I got about what I paid for them in 1960's $.
I kept some, a bl.p M2 and some M3's. Still works after having shutters replaced.
If a camera works, keep on using it until it doesn't - the cost of fixing something minor is usually 30-40% of a full overhaul anyway, so you might just as well justify it.
Leica is fairly unique in high priced gear as there are still Mint, boxed, unused etc. cameras around, these have sat in boxes for 20-30 years and everything is getting "gummed" up. Thats when you need a lube-job and, if unlucky, a shutter blind replecement as the compound on the cloth can dry out and crack.
When I get a new "used" body - I shoot a couple of rolls with it, cycling through all the speeds. It they are OK - I keep using it. If there are issues with them, I have them adjusted. If everything sounds dry and squeeky, an oil-change. If finders are dim or out of whack, beyond "self-fix" - I usually abstain, unless the price is good enough to have a full repair done.
Some years ago I picked up a M2 (surprise!) in Germany. I checked the shutter and it was dragging badly at 1 sec and capping at 1/250 and above. No big deal, I assigned it to a 21mm VC and used it in the functional range for 3 weeks and then had it adjusted when i came home.
One problem is statements "Just returned from CLA" and subsequent price hike. Fine, if it is accompanied by an itemized invoice, stating what was done and by whom.
Yes, if I find a camera that has a recent overhaul done by Jerry at Kinderman, DAG or Sherry - WITH said invoice copy - I would trust it and be willing to pay the extra.
Most of our cherished M's (M2/M3/M4/M5) are getting on in years and some kind of service could be needed - but if it works when it ends up in your hand, just keep using it until it really needs it!