Blue Devil,
The only way to visually differentiate between a '92 and '93 500E is the brake calipers..MAYBE.
'92 and early '93 were equipped with black paineted, Brembo, 4-piston, aluminum calipers. These were sometimes problematic and later cars were upgraded to 500SL and then 600SL brakes which are cast iron 4-pots made by ATE. The 500SL variant has 300mm rotors while the 600SL brakes are 320mm.
The '92 has a little bit more in the way of horsepower...approx 6 bhp more if i remember correctly. the 92 has 322 bhp while the '93 has 316 bhp or so...officially these are the numbers. But at over 310bhp does it REALLY matter that much when you're not on a racetrack?
IMHO I'd rather go for the later model as these are the ones in which the bugs have mostly been worked out.