CDT, just a parting thought -
A problem I and many others have run into is worn keys/tumblers for the exterior and ignition locks. My experience is that the problem is worse for the MB design than other makes. One way to reduce wear-and-tear is by installing a keyless entry, which I did. That won't restore the damage to your keys, but it will extend their useful life when they no longer are needed for access.
What you will have to weigh is the cost of repairing your vacuum leaks vs. new coded keys and lock tumblers at some point. Admittedly, I haven't any leaks yet, so the $50 keyless/alarm cost and man-day for installation are a cheap preventative.