Microwave fuse blows when closing door

Panasonic NE-1054C microwave is 3 years old.

Came to me with a blown fuse. Disconnected power, checked HV capacitor was discharged, and began troubleshooting.

- Tested the 3 door switches and power relay connected to PCB. Switches tested correctly with door open and closed, multiple times.

- Checked door latch alignment. Nothing loose or out of alignment.

- Checked for signs of loose connections, wiring issues, burns or signs of overheating. Everything looks good.

- Checked all other major components for possible issues, shorts. Nothing found.

Replaced fuse, button-up cabinet, connect to power, open and close door multiple times, place a cup of water inside cabinet, run for 30 seconds (do this multiple times switching out cups of water) and it works.

Return microwave to owner, owner uses for one evening several times, no issues. Tries to use in morning - dead. Assumption is that last operation of microwave in evening blew fuse without owner noticing.

Pick up microwave, find blown fuse, test switches again. Switches test proper. No visible signs of excessive heat or problems, no components test failed or shorted. Close up microwave, connect to power, run for 30 seconds with cup of water inside, open door, close door, run for 30 seconds again, open door, close door - FUSE BLOWS.

Has to be a door switch - test all switches, again. This time I use an analog meter to see in real time when switch opens and closes. ALL switches work without delay. Power relay contacts are in OPEN position, as they should be.

3 mechanical switches and one electrical relay involved with the door function:

- Primary interlock switch

- Secondary interlock switch

- Monitor switch

- Power relay on main PCB

​I am at the point now where I am assuming that the circuit board is intermittently glitching causing the power relay contacts to CLOSE when the door is closing. This would cause a direct short and blow the fuse (I tested this by disconnecting the power, disconnecting the leads form the power relay, putting a jumper across the leads to simulate CLOSED contacts of power relay, and then closing the door with a meter connected between L1 and N - meter goes to 0 ohms/dead short). But I can't prove it under power which is why I am hesitant to just throw parts at it to attempt a fix.

3 switches = $60.79 CDN before tax and shipping

PCB = $128 CDN, out of stock

Parts found here:

https://www.partstown.ca/panasonic/ne-10...

I could risk $60.79 on switches that appear to be working just fine or $128 on a PCB ( if I can actually get one) that I can't guarantee is the source of the problem. No smoking gun and no desire to waste money.

Any suggestions for troubleshooting this issue further? Thank-you