I am wondering if the O rings used in the engine eg. water/oil pump between the block and the pump around the coolant passage, are made of a particular material???
I am replacing an output shaft and have all other consumables on hand.
I would like to source the O rings locally but not sure if they are a particular compound eg. nitrile or vitron etc.
The ones from the usual suppliers are usually Red but when I have bought them locally in the past they are black.
Does this make a difference ???
I am in OZ

A compatibility chart  will give you the basic material compatibility.

In general, nitrile and viton are good for oil and coolant. Use EPDM for brake fluid.
Nitrile and viton would traditionally be used with gasoline but these can be adversely affected by ethanol. FKMs (flouro compunds) and HNBR (hydroginated nitrile) are more resistant to heat and often used for engine seals and o-rings.

You also have to consider hardness.: typically an o-ring will have a shore-a hardness of 70, and temperature range. Some materials, e.g. PTFE, are resistant to most chemicals and have a good temperature range but are very stiff.

As for colour, typically nitrile/NBR is black, viton is brown, HNBR for aircon is green and silicone is red. But I wouldn't rely on it.

It is probably wishful thinking that the OEM material is the best for the job; your bike's well out of warranty so they don't have to fix it and there's no guarantee that what you get these days is original spec anyway. But to play safe, I'd say use OEM for things that are hard to get at, go your own way if it's cheaper for accessible seals.

The only advantage to getting seals locally around here is that I don't have to wait for the mail from MaxBMW.  Prices from BMW are shockingly similar to what I pay for seals and o-rings at the local bearing supplier.

I'm fairly sure Inge said they were silicone but I have used the black nitrile O-rings there and not had any problems.

Thanks for the info
Couldn't find anything locally so have stuck an order on with Munich's