Sparks and loud hum from oven

1. I went to the internet to find the service manual for the Maytag microwave.
2. I opened up the oven and started measuring the resistance of the diode, capacitor, transformer, and magnetron between terminals and then to ground. The transformer and magnetron were well within the resistance limits. The diode was shorted in both directions(+-). The capacitor was fully open in both directions -- high resistance.
3. I ordered the 2 parts, installed them, and ran the oven. Worked perfect first time.
4. Reinstalled oven and worked ever since (1 week so far).
5. The secret was that the transformer had a load hum. I figured the transformer was OK. The magnetron had no short between filaments and ground to filaments. The only two left were the diode and capacitor. The first two are about $200 -- almost the value of a new microwave. The $70 repair was well worth it. If the first two were still bad, then tempted to buy a new oven.