unfortunately the tensioner and belt took 3 hours labour time, and the tensioners themselves are the expensive bit. All in all it came to around $400 for that repair, though if you only need a belt and can change it yourself it'll be about a 10th of that cost! It did make the steering feel much better and stop the squeaking i had on start-up nicely though:-)
I'm fairly new to the 300e so one of the senior members will know more on how to replace it yourself I'm sure...

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1993 320TE M104
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past:

1983 230E W123 M102
1994 E300D S124 OM606 (x2)
1967 250SE W108 M129
1972 280se 3.5 W108 M116
1980 280SE W116 M110
1980 350SE W116 M116
1992 300E W124 M103
1994 E280 W124 M104
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"music and women I cannot but give way to, whatever my business" -Pepys