If you don’t have proof of purchase GE will go by the manufacture date unless they have a record. They will have a record if you sent in the warrant card or had a warranty repair in the past.

Customer relations might send you a magnetron tube if you ask, but typically you have to have an authorized servicer to make the repair. This will still most likely be cheaper than if the part wasn’t under warranty assuming the magnetron tube is the problem.

Thanks Applianceman & Shawn for this VERY helpful thread - I think we must have bought in the same development in Utah? Moved into a brand new home in 2006 and paid extra for the kitchen and for Stainless Steel appliances. All GE. We have had nothing but problems!!
Thanks for your help and suggestions. I am calling GE to see if our Magnetron is under warranty on our GE Spacesaver Microwave XL1800. Just stopped heating tonight. Tried all the tests and tricks.
GE service guy was here just a few weeks ago since the heating coil in all the dishwashers made that year was recalled. Nice. Our dishes have all that white stuff on them too, so I'll try the citric acid. The dishes still don't dry though.
Any other suggestions would be helpful, other than is there a class action lawsuit going against GE for their faulty appliances. NOT TOO HAPPY about this...
Oven and range are really not that great either. GE stinks.