The worst possibility is if there are a large number of small pinhole leaks due to corrosion of the pipe.

I would check all the wiring, plumbing, mechanical systems closely for corrosion.

They claim it was due to corrosion.

Aluminum is rather an active metal for such application - might be given to cathodic corrosion issues.

He said there was more corrosion/rot than he realized, and he now needs to replace the sliding door.

If they are older metal pipes do you see corrosion or rotting pipes?

Typical Honeywell Thermocouples are sprayed with a little bit of oil during packaging as to protect from corrosion.

You can also see superficial corrosion of supply line connections.  

I believe the current fix is to crimp on pigtails to all ends and replace the old switches and outlets... varies but think it is running $2500 to $5500 per house to correct... aluminum vibrates when it gets a little loose causing resistance and then heat.. hence the problem.lots of homes have black pipe or steel pipe water lines used a lot in older homes and it is OK but it rusts inside and then as the corrosion continues the pipe gets weak at the joints mostly and often can fill up  and restrict water flowall this being said I have seen extension cords run behind finished walls,  I have heard people removing 40amp breakers and replacing with 50amp breakers because the 40amp keeps tripping.  

You also need to blow out the dust/corrosion in that panel & add some anti-corrosive/connector gel.I replaced several 100 amp breaker panels over the last 12 months for this reason & to remove random sub-panels that were not to code.