I didnt know mechanic's delivered parts
according to this site , the total number of 3000gt's sold was 79,536. Total number of Stealth's was 63,296, for a combined total of 142,832 3s cars sold in the US.
Unfortuanately, I could not find the sales numbers for all the DSM's, but it wouldn't surprise me if there are over 100,000 turbo AWD DSM's that were sold in the US, plus the other variations. IMO, a 10 to 1 ratio of DSM's in the shop to 3000gt's in the shop sounds dead on for their reliability.
But then again, you are comparing DSM's only to 3000GT's. If you were to add Stealths into the equation of 10 to 1, then that would be 10 DSM's to 2 3s cars, which equal's a 5 to 1 ratio. That sounds a little more realistic to me.