Without looking at the exact circuit I can't say how the relay problem influences your car. These relays were mainly for emissions control and weren't present on early models 220/8 and 230.
If I remember correctly your problem was extreme. I hate to second guess your tech but whatever the relay is doing wrong could be by-passed for diagnostic purposes in my opinion. This allows you to move to the real problem without delay or expense.
I worked in the dealership when your car was built and have worked continously on MBs ever since and have never replaced one of those relays. Probably because their effect on running right or wrong is usually insignificant.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician