Well the shop called back this morning, and it looks as it you were right!! (I did mention that possibility to the Service Guy when I took it in.)
They got the EGR error code again, and checked the vaccum lines, which had become restricted, cleaned them out, did a 40 mile test drive and it seems fine.
Final Bill - No Charge!!!!, and bring it back in if it happens again. For those of you interested I took it to Park Place Mid Cities Mercedes (formerly Becks)in Bedford-Euless, TX (Just near DFW) they are not the cheapest, but it is one of the Biggest MB dealers I have seen either here or Europe.
Thanks to all for advice and suggestions :-)