Those popular ones that look like this:

Turns out that any biodiesel getting into them is rapidly fatal.
7 is a very thin EPDM value in the shape of a disc, well, afterwards, in the shape of a cabbage leaf.
And now the windings are all filled with bio as well, and several other rubber bits failed.
Oh well, it's done me for years, time to get a new one and mount it above the things it bubbles this time...