Electrics: XC70 2.4 D5 (2007) - ECU fault?

[Headhunter]

Hi, I have a wonderful XC70 D5 (2007), 85k miles, but recently it has a recurring fault:
It starts with a slight misfire, then next time I start the engine it comes up with various faults on the dash (engine, antiskid etc), the auto box is stuck in 3rd gear and the misfire is worse, though the car will run (just).
I called the AA who thought it was a sticking swirl valve (apparently creating a domino effect of other fault codes).
The local Volvo specialist adjusted the swirl valve, replaced the glowplug on injector 5 and cleaned all the connectors on the ECU which cured it for about a week.
The car sat unused for a couple of months (during lockdown) then the problem reoccurred.
The local specialist recleaned the connections on the ECU and the car ran fine again for a few days before the problem happened again.
Now he says it is likely the car will need a new ECU (not cheap I believe).
Any suggestions please??