Thanks for your comments
I also wondered about synchronisation as this would show similar characteristics, although I'm not sure of the red light staying on and the remotes is brand new - having said that I'll force a re-sync to see what happens.
Steve - Startek doesn't seem to provide that much info (reviewed the demo) and it's USA born, perhaps there's a euro equivalent?
'93 R129 500SL-32
'89 190E 2.6 - sold in 2002