1986 2.3-16V Chain Tensioner -- Price Is Right???

Hi Guys:

I was just reviewing some repair documents that were furnished by the previous owner when I bought my car (back in February 2000). Back in August 1996, one Repair Order (from MBZ West -- Specializing in Mercedes Benz) shows the timing chain AND tensioner being replaced at 67,436 miles.

[1] Timing Chain $30.00
[2] Timing Chain Tensioner $380.00
[3] Install modified tensioner $200.00 (labor)

The Order does not say anything about Chain Rails being replaced, so the questions are:

[a] What was/were the problem(s) associated with the "factory" chain tensioners? I heard it was one of lubrication, and also heard one could modify the existing by drilling a small oil passage hole (?)
[b] Are there inherent problems with factory chain rails, or were they failing because factory tensioners were not being changed?
[c] In your opinions, at 67,000 miles on the factory tensioner, will that have created any problems with the rails? FYI, the new tensioner has been in place 20,000 miles and I have not seen/heard any problems.

Also, what indicator(s) can I look for to see that the tensioner is, in fact, the "upgraded" version?

Thanks!

Brian16V