That's the so called "resin rot", that will affect 99.5% of older models. There's no way to avoid it and the only remedy is to get a new set of resin. However, I wouldn't use soap, neutral or not, very often on an old model. Get it clean once and baby it afterwards (use it sparingly). If you frequently use soap to clean it you will accelerate the natural decaying process of the PU resin - the same goes for sun or UV radiation exposure.have seen a lot of old Casio straps an bezels, that they become totally greasy and slipy if the get contact with water or humidy.
-What can this be and why?
-How can I stopped it?
It wasn't limited to Gs either. It basically said "If you don't pay as extra to check the insulation rubber we can't guarantee anything". Made me wonder if that was common practice among watch repairman... I guess it's not. Anyway, this one won't see me again."Kind" of ridiculous? They should put a sign that says "Bring your watch and we'll rip you off".
A watch repairman who can't guarantee that a modern G Shock he worked on is waterproof after he's done with it should not charge for any kind of service. You don't need to pressure test the watch if you know what you're doing. If you do need to pressure test a modern G after you worked on it you shouldn't even have started to work on it.