My 1988 560SL wouldn't start when hot. It got progressively worse. After one mechanic changed the fuel filter, 2 fuel lines, accumulator & a start valve (for over $1000 & all to no avail), I took it elsewhere. They found that the intake seals were leaking. The second mech troubleshot it & fixed it, but the fuel injection was out of adjustment (probably the first guy who worked on it). After much tinkering (and $1894.77), it's running like new. The first mechanic was going to change the plug wires even tho I told them they were new. Long story short, find a good mechanic who knows what he's doing!