[ngoma]

That T-stat appears to be the correct one. We don't see them with the bleeder orifice (should be oriented at the 12 o'clock position) and it is not really useful in our application. Did the new T-stat have one?

Probably the encircling seal instead of the simple o-ring is OK as long as it seals sufficiently well inside the housing. Disc to be installed facing toward the engine block, ya?

The 87 imprint is, of course, the temperature rating. I don't know what the other number is. The one I am looking at currently (much newer, as it says "Made in Germany" vice yours "Made in W. Germany") has a "07 09" stamping opposite the temperature rating.

Good on you for testing the old one-- keep it as a spare.

If you like we can compare dimensional measurements: disc diameters, and disc to disc height.

There have been some isolated reports of defective water pumps. Not so much corroded impellers, but impellers slipping. As you imagined, there is no easy/painless way to verify this. I guess just to continue systematically verifying all the other factors are in good working order.

ALSO: Brickwerx lists the WP version that has less cog teeth. You may ultimately want this for its theoretically increased output for a given engine speed.