2001 C220 diesel auto gearbox problems

[DCMAN]

New to this forum so excuse any mistakes. Recently purchased a used 2001 C220 estate for just shy of 5k (full MB service history 114k), as a new family motor thinking them to be reliable and well built. After a couple of weeks the auto gearbox started sticking between 2nd and 3rd and sometimes dropping out of gear all together (which was'nt good when trying accelarate from a junction). Took it to a local garage who serviced the gearbox. On the way home near my house gearbox stuck in 1st and would'nt change. Go it towed to a Merc specialist who said I needed a new gearbox. After a week got the car back (1200 quid lighter). Was fine for a couple of weeks then broke down on the M6 with the same issues, this time gearbox clunking heavily into 1st and not changing. Got it towed again to the Merc specialist who gave me a 12 month warranty on the new box initially. After a week he has told me it needs a new ECU. This is probably going to cost me a few hunderd quid to. Just need to know if this is an inherant problem with these cars, or after getting it sorted will it do 200k plus which I got out of my old A4 without it missing a beat. If I keep it how can I stop this happening again. Cheers.