I had a 103 engine car in my E300 '87 that got to missing at about 90K and required a replacement of dist cap.

More recently, at 60K, (with no running troubles), I decided to check the dist. caps on a my '95 S-420. There was some dirty green tracking around the posts. I cleaned this off with laquer thinner and a strong bristled tooth brush. Once clean, I tried something that I had never heard mentioned here, (or any where else). And it seemed to work great -- I'm now at 113K and still having no troubles at all on the original caps and rotors.

What I did was spray on two coats of "Conformal Coating" of the type that is used on electronic circuits boards (computer motherboards, etc.). Its a clear very hard coating that has high die-electric properties. I'm hoping that it will hang in there a long time and stop the "arching over" that is the typical failure mode of these dist. caps.

The caps were kind of high cost to me so I thought that might avoid the need to replace.

What miles are other people getting on theirs ? I doubt it matters how you drive. Perhaps dusty conditions could affect it some ?

Luck to you,
DanielW