Yes, new valve cover seals should have been part of the job. They are soft and pliable when new, but become hard and brittle with age. I've read that if the seals have been on for 3 months and the cover is pulled, use a new seal.
When I did the timing chain on the 4.5 last weekend I used new seals. The old seals had been on for almost two years, were still pliable but had a definite indentation from the head, even after being off for a day.
Passenger side cover is a piece of cake, just the four bolts (10mm). Driver's side requires removal of the brake booster vacuum line and the fuel lines from the fuel cooler to the fuel distributor, plus the four bolts.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.