My type M is about to be replaced.
2 seasons ago, it was sticking open, so I put a little machine oil on the pins. Must've been too much, as it collected ash and then barely functioned. Multiple cleanings, even with cigarette lighter fluid to remove the oil and a wire brush slowly improved its functioning.
Then I made the mistake of hitting it with LPS-3 when I shut down for the season. Last season started with a re-cleaning of the damper, etc. It worked better than the prior season, but still got stuck wide open a couple of times. Last season shutdown, I did nothing to it. Just left it in the cleaned out flue pipe Tee.
This year is a disaster. It seems to operate sluggishly. On somewhat gusty days, it only moves a little, whereas in prior years, it would be going almost max open to max closed. Last night, it did it...stuck open. The house stunk a bit, but no CO on either of my 2 digitals and none of the 3 other CO detectors went off.
This weekend will be my first shutdown and cleaning of the season. It gets one more cleaning and one more chance. Then I spring for a new one!