i don't think the reason for bringing 500sl's from europe was to get the extra hp. if i recall correctly, in the 70's and 80's there was a huge savings to be had if you purchased the car in europe, drove it 1000 miles and imported it as a used car. savings would have been around $5000 along with a free euro vacation as part of the deal. u.s. customs allows exception of only one car per household during a lifetime so dealers would bring in a boat load of mildly used euro cars under a different owners name for each vehicle and throw $1000 to people who allowed their names to be used on the temp title.
personally, i think the 500sl has the advantage:
- without cat converter the exhaust is straight thru and no add on monitoring O2 equipment
- headlights nicer, bumpers nicer and lighter on euros
- climate control system (i believe?) were simpler on euros because they had manual controls
- you get the rear fog light on euros. not much use but i'm always one for another toy.

also, i dont think repair on gray market car would be an issue. the 500sl body is mostly like any other sl. as for engine, we have 500sel's which, i think would solve any engine/transmission needs thru MB supply chain.

jack