Service (??) of Datejust

[Lawolf]

Hello, everybody!
I'm facing a serious problem and I would like ot ask for your assistance.
I own a Rolex Datejust dated back to 1967-1968. I sent the watch to Rolex service center for maintanace once it hasn't been serviced for a while. Please note that the watch was working perfectly till then (functional and water resistant). As a standard procedure, the service center checked the watch and inform me that some parts will be replaced due to normal wear and that after the service the watch will be accompanied with 2 year warranty.
I just received a call from Rolex today, stating that the watch cannot be water resistant any more because one membrane that is used for sealing is out of production from Rolex, so my watch will never be waterproof again....

Has anybody faced the same problem?
Any suggestions?
Are you aware of any 3rd party source, where I can find this part?

Thanx in advance.