problem identified

[dtrain]

I posted a thread several weeks ago concerning my '89 420 SEL having a rough idle at when I started the vehicle. I checked several avenues that were suggested and nothing turned up until I started the car yesterday and it wouldn't turn over.

I had a mechanic take a look at it and he determined that the timing chain tensioner had broken. He also said that the timing chain was on its way out and at least two of the plastic guides were broken.

He claimed that the links were jumping when the car was idling upon ignition and that as the rpms rose, the "roughness" would disappear because this could not be detected at higher rpms.

Does this sound legitimate? I am supposed to see the car tomorrow morning. His price tag for fixing this is around $1,600.

If this is indeed the problem, is that a fair price for fixing it and could this be a diy job for a fairly amateur mechanic?