Sorry to read the Koni experience didn't live up to expectations.
Frankly I am not surprised based upon a personal experience with their shock absorbers.
Back in the late 80's I did a series of Railbus trials here in the USA mostly down the east coast.
It can be said that the track conditions are generally not as good as Euro rail systems where passenger traffic does not mix with freight. Consequently the suspension was subjected to much higher reversals on class 3,4, & 5) than was experienced by similar operations in Europe. (exception the AMTRAC dedicated lines from Boston to Washington DC. (then class 7)
It didn't take long for their shock absorbers to blow their guts out once we had the unit in service. Even being from a large multi national corporation we didn't get much sense out of them quite frankly. Looking for a quick solution when I got to into Virginia I contacted the Monroe group who within a few days supplied us with some "one off units" which I installed in Winston Salem & lasted for the remaining two years of trails across the USA.
From then on I have never recommended their units, the standard fit is Monroe as far as I can see on production Sprinters, although I have been installing KYB due more to availability than anything else.
Dennis.
ps
For curiosity sake, here's a piccy of the said Railbus now back in the UK with a private line operator.
The top left picture is the unit with SEPTA on the Newtown Pottstown branch line---Yours truly at the desk in the middle.
https://www.google.com/search?q=bre...YH5D1oAS1yIG4CQ&ved=0CFIQsAQ&biw=1296&bih=705