Patrickh
During normal (standard) service, I suppose they control movement and waterproofness.
It is the standard practice for watches to be tested for performance and water-resistance before shipping out but sometimes things can fall through the cracks. The better the watchmaker, organization, or QC department the fewer things fall through.
Did they change oil EVERY TIME (systematically) or only if specify by owner or requested by their examination?
Did they dismantle (take to pieces) all the movement at each control visit?
Yes and No. For watch services list as full overhaul, full service,
complete service or something of that nature, the normal procedure is to
dismantle, clean, assembled and re-lubricated the movement. Then it is
adjusted, timed and regulated. The case is sometimes refinished and new gaskets
are installed.
Some companies offer something commonly referred to as a basic service. This is
for when the watch is in need of a regulation or other minor service but does
not yet need a full service. This is typically done at shorter intervals than
the recommended service intervals (1-2 years). It is typical of this type of
service to replace gaskets, clean and oil the balance and escapement, time and
pressure test the watch. This can get the watch "freshened-up" as far
as timing is concerned and insure proper water-resistance with new gaskets.
Only some companies offer such a service and those that do only offer it at
their option. I cannot tell you how many time a customer has told me that
it just needed freshening -up or the oil topped off when the watch needs
to be taken off life support. Not all movements are designed for this
service to be completed either. The 7750 for instance does not have a separate
escape wheel bridge to facilitate the removal of only the escape wheel.
I hope this answers some of your questions. Basically, the watchmaker working on the watch will use his or her judgment as to what the watch needs. Since you are at the mercy of the watchmaker and need to trust them, it is important to do your homework and find a qualified watchmaker with good references when not sending the watch back to the factory service center.
I am glad you enjoyed the article and I am sure you will find other great resources here to further your watch knowledge.
TCP