We had the exact same problem with the boiler - of a similar age - in our old house. The engineer tried numerous times and ways to fix it, including three replacement thermo-couplers. He said the wind in the flue shouldn't be a problem because boilers are meant to be built to withstand that. In the end, nothing worked and we had to have the boiler replaced. The replacement worked perfectly and no adjustments had to be made to the existing flue.
Can't remember the name of the old boiler (not the same as yours, though) but the engineer did say it was one of the worst brands/models around and he was surprised it had lasted as long as it did. Replacement was a basic, Worcester brand combi-boiler, apparently very much liked in the domestic heating industry.