Master Brake Cylinder Diaphragm blues...

I got a new diaphragm last year and now it´s like a swollen whate and won´t fit.
What is wrong? Rubber material or wrong .dot? I used 5, but the rubber must be of the
right kind too right? Where do I but good ones?

Did you use OEM parts?  The stock system is rated for DOT 3 fluid.  DOT 4 is okay too.  I've never heard of DOT 5 causing problems but maybe?

wrote:

Did you use OEM parts?  The stock system is rated for DOT 3 fluid.  DOT 4 is okay too.  I've never heard of DOT 5 causing problems but maybe?

I would if I could, do you have a source for that? I tried Ebay now and I found one seller and I´m pretty sure their gasket is not OEM,
probably like the last one that´s inflated by brake fluid now.

What year and model?