Is my Magnetron failing

Hi Team - I have an NN-ST656W 1100W inverter microwave. I recently fixed a plastic part in the door release and got another 18 months out of it but its starting to overheat and stop cooking effectively.

Basically if we use it to heat something or cook something quickly it works as expected but if my wife cooks pasta in it that has a volume of water it works well but then when she goes to cook some vegetables straight afterward she'll put them on for longer than she normally would and they are still al dente/crisp. At this point the body of the microwave is getting quite hot.

I initially wondered if the cooling fan wasn't working but once I had the microwave out of its shoulder high posi it seems to be moving air well. I've swapped it with the Samsung from my office as at work I only heat a Frozen meal or a pie.

That leaves me thinking its probably the magnetron getting tired? Does that fit, I don't want to waste ~$90 NZD on a part as a new similar 32L microwave is only $250. Otherwise, I'll just keep using it to heat Macaroni and Cheese until it gives up completely. I've lost track of how many years old it is - It appears they still sell the same model now and I've lost track of when we got it - It feels like it could be 10-12 years old?