Proper torquing of the delivery valve holders after a seal replacement is very important. There's a 3-step torque process to ensure that the sealing rings are seated and properly mated to the delivery valve holder. Too loose and the DV leaks, too tight and you run the risk of damaging the pump.

I have no idea what "levels" the first guy was talking about.

R&R of the DV seals can be done with the intake manifold in place, but it's a massive PITA. More than likely, his labor costs involve removing and reinstalling the intake manifold for better access. If they're removing/reinstalling the manifold, changing the fuel supply hoses, and changing the filters for you, I'd expect the labor to come in somewhere around 3-4 hours + materials.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]