Are they a Twp part bit? Like oil water pump sandwiched together? If so, since it looks like mine is leaking oil, how much of a pain is it to change the seals? And what do I need to do as well as seals?

85RT is likely to have the 'old' impeller and nut arrangement. It is a single shaft that functions for both oil and coolant. The usual tell tale is the drip at the front of the engine.

Apart from the seals the impeller is likely to be gone, the nut arrangement inevitably breaks off and anyway the shaft is likely to be worn or pitted. When I got mine done it was a case of new shaft, impeller and seals. The shaft and impeller were modified by BMW and you will be getting the modified version where the impeller is bolted on.

Its a tricky job as there is a ceramic seal that is easily damaged so you need to be careful putting it all together. There are some excellent threads on doing the job.

It's not leaking coolant. I thought it was leaking oil but I am pretty sure it is not oil from the pump but from the old timing case cover.

They are the one unit with the oil pump behind the water pump. The usual drain the water and remove at least 1 litre of oil before removing the pump.
Remove the nut holding the impeller, it may break off which will mean a new shaft around, 100quid, then press the shaft out remove the water seal then the oil seal noting which way round it goes. Inspect the shaft which will probably be pitted but check the area where the seal runs it is often OK.
You will probably need a new shaft and definately a seal kit. you can use a new impeller or machine 3mm off the boss of the old cast impeller and use it.

"I thought it was leaking oil but I am pretty sure it is not oil from the pump but from the old timing case cover."

Degrease the whole area, go for a ride and see if you can spot where the oil is coming from...as a suggestion.

What Mr. Blakey said - degrease the whole area and watch for the pattern of the oil splatter.  The airflow over the engine does odd things with oil as you ride along. 

Are you getting oil on your left boot?  If so it could be the camshaft cover leaking at the front where it joins the timing chain cover on the LHS.  There is a bit of a mismatch where they join and there are specific instructions in the Haynes manual stating to apply sealant where they join when refitting the camshaft cover.

+1 on tackler's comment about oil on the right boot. The oil pressure sensor in the oil/water pump is another culprit for oily mess in the pump area.

88 wrote:+1 on tackler's comment about oil on the right boot. The oil pressure sensor in the oil/water pump is another culprit for oily mess in the pump area.

Funny that, same way I knew my push rod seals were leaking on my 77 R100rs!

Turns out it was the timing cover before I did all the work, it's all dry now.