GMT case back seal question

[terryuk]

I want to replace the gasket between back and case, but I'm not sure if the correct one is the 'O-ring' type or the flat gasket type.

The watch is GMT 16750, numbered 6.27million year 1981.

I assumed that it would be an 'O-ring' but looking at the one in the watch, it appears to be flat and quite hard.
I can't beleive that age and compression could change a cylindrical section into a rectangular section and make it like plastic instead of rubber...

If anyone knows what the correct part number is, or whether the flat type gasket was ever used in this model, I would appreciate your input.

Thanks

[shofzr]

29-325-10
O-Ring Gasket


Sent from my iPhone using Tapatalk

[J!m]

Yep. O-ring; and yep, they get petrified.

Not in watches (yet) but I have had old o-rings so brittle they litterally snap and crumble.

[terryuk]

Originally Posted by shofzr

29-325-10
O-Ring Gasket


Sent from my iPhone using Tapatalk

Thanks for that. I'll order some from Cousins UK

[terryuk]

Originally Posted by J!m

Yep. O-ring; and yep, they get petrified.

Not in watches (yet) but I have had old o-rings so brittle they litterally snap and crumble.

Ok, this one was like hard, brittle plastic... had to literally 'chisel' it out of the groove ( used an improvised brass tool so as not to risk possible damage)

[J!m]

Ok. Totally plausible. it might not be a bad idea to soak the mid case in acetone and use some q-tips to clean out the groove after it soaks for a while. Try not to use metal (even plastic can be a problem)to clear the groove because you can scratch it and reduce the ability for the o ring to seal. Surface finish is pretty critical.

[terryuk]

Originally Posted by J!m

Ok. Totally plausible. it might not be a bad idea to soak the mid case in acetone and use some q-tips to clean out the groove after it soaks for a while. Try not to use metal (even plastic can be a problem)to clear the groove because you can scratch it and reduce the ability for the o ring to seal. Surface finish is pretty critical.

Thnx Jim, it's pretty spotless now.
It wasn't actually stuck to the metal, but somehow compressed, filling the entire groove - made it a little tough to prise out...

Thinking back, the only time this watch was out of my hands was twenty years ago when the Rolex dealer in my home town had it for a week - he also put a new crytal, but I'm wondering if he put a flat gasket instead of an O-ring.
Oh well, no big deal...

[J!m]

Naah. Totally normal. I rings flatten fairly quickly. This is one big reason why you should test annually if you intend to use it to its fullest water depth potential.

Just because it has never been opened, does not guarantee it is still sealed.