Is there a rule of thumb on when to replace the gas diffuser in MIG torch?

I replaced mine last night - for the first time ever. I've had the welder for a few years but probably only put about 50kg of wire through it.
I'd been having some weird arc stability issues, ground was good, tip replaced a couple of weeks back and not showing any signs of wear etc.

After replacing the diffuser everything was fine, but I'm not sure if a diffuser could cause that sort of behaviour, or if the improvement may have just been a byproduct of pulling the bits out of the torch to replace it.

Old and new for reference:




Steve


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