Yea, they do change some parts, even those that may cosmetically be different from the original eg. service dial, etc. Some may be highly sensitive, especially those older sports models like Subs, GMT-Masters...
I'm also considering if I should send in my 216570 for service soon...RM2.5k - including some change of some parts, including the crown, seals, balance wheel (I think) - according to RSC. Only concern about independent watch makers is that they may not actually change parts - you won't be able to tell unless you open the watch. Unless as mentioned, they are someone you can really really trust.
Just my 2 cents...i'm in a dilemma myself