Renishaw TR1 diaphram

Hi,
I have a Renishaw TP1 probe I bought on eBay for buttons and found it remarkably easy to rebuild apart from the diaphragm that protects the innards from dirt. Could not find a spare on Renishaw site but looking at their prices for other simple stuff I could not afford it anyhow.

I tried using a no 2 baby bottle teat which if turned outside in with a hole punched in the end is the exact size required! Thought I had cracked it until I tried it out and the teat is too stiff causing the contact to be permanently open.

Don't want to spend too much time on this as the probe works fine, on a resistance meter, without a diaphragm it's just I can see it failing at the worst time due to a bit of dirt in the contacts.

I had thought of using a condom but somehow I baulked at the idea and its probably too flimsy? Will it tear if a hole is punched in the end I'm not sure I want to know.

I'm stumped and looking for something to adapt.
Thought about glove fingers and even latex dipping a custom mould but I just don't want to free up the time it will take.

Ideas?