MB Vito 112CDI Dashboard Fault

Just bought a 2000 Mercedes Vito 112 CDI Van 123k miles (5 seater with window side doors) - with the cold weather we have had over the last 2
months, the dashboard has developed a fault (only when cold) the rev counter and speedo dials move up and down in time with the dash lights flashing and the clock has reset - took to MB dealer who could not replicate the fault even by discharging the battery and they say it is the dash but this will cost about £600 (claimed not to have seen this before but there was another Vito owner in with a similar faulty!) - this happened to me last week when de-icing the van and I couldn't get the rear heated window to work. When the dash stopped flashing the heated screen then worked. I don't understand how the faulty dash could affect the rear screen. We also get the central locking to unlock when driving randomly. Does anyone have any ideas before I get the dash done and then find it is not the dash that is faulty and a waste of money.
Thanks in advance
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