I can only speak for the 90 thru 95 300SL which I am familiar with. The engine is a 24 value version with valve timing. The automatic transmission is a 5 speed, but starts in 2nd gear unless punched or manually over-ridden. If your RPM concern is gas mileage, I get about 19-21 mpg overall mixed driving, but 25-27 mpg on a steady highway trip on my 91 300SL ( 129). The 129 can be fitted with an after market rear seat, but it is a bit of a joke, as only a small child could fit back there. Some mid 90's models of 129's have wiring harness insulation problems. Do a forum search. After 95, there were major changes in the engines. Eventually the 300/320 engine was dropped because the new 500 engine offered comparable fuel enconmy.

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