The Clymer manual is a good choice. They are not cheap but if you look you may do better than $47.95.
There is also the Haynes manual that I have heard some prefer.
It might come down to shipping charges, which one is cheaper? The Haynes is $45.45
There are shop manuals published by BMW. I couldn't find one for /5 vintage but think it does exist. Still if you found this it would cost a Hundred dollars or more.
Both these sources you have been given are the actual publishers web pages. For some reason you may find these same manuals cheaper from other sources.
I have both of these and can't really say which one I prefer. I think I use them all. There are also many web pages and blogs on the web. There are 3 or 4 forums that will help walk you through the process.
We will give a lot of help here at Adventure Riders but really want you to get the manual so we don't have to repeat too much stuff. Rear main seal will mean taking the clutch off to get at it and you will be checking the clutch for wear before putting it back. Most of the time this job requires the replacement of the clutch. There are alternatives that save a little bit of moola but it ain't cheap.
How many miles on new machine?