Hi, as this is my first post after the introduction I hope I get this correct.... ...I wonder if I could be enlightened on the small breather hose that runs from the crankcase to the air box. I gather it is somewhat important and needs to be crack free...also is there any cheaper substitutions that anyone has come across or is it BMW prices and nothing else...thanks (1991 K100RS)

Have a look at Motobins and Motorworks in the UK.  Both around the ten quid mark, so if buying one at current exchange rates it will land on your front door for about $30. 

Nothing aftermarket that I have found although possibly cheaper in the USA.

Just one of those parts you need.  So buy two and put one in the cupboard 'cause next time you need one the price will have gone up.   And they go on one way only.

Another source:  Munich Motorcycles in Perth.

Engine breather hose

blaKey wrote:Another source:  Munich Motorcycles in Perth.

Engine breather hose

That is for a 2V, OP has a 4V which have a quite different hose.
Actually it's 4 different hoses in the breather system, sooner or later they all go bad.


Same hose (closest to the crankcase outlet stub) on a 4V:




And no I don't have any good suggestion for an alternative to the OEM part.

Oops!

Thanks Inge.

at least they are identical in one end.