Hi Mike & Lynne,
Just found a picture confirming the original microwave. Most that I had appeared to show the same microwave, but the pictures were to small to tell what kind it was.
The original microwave was a Dometic RV Microwave.
I suspect the original unit died and the owners just replaced it with what they could get at the store instead of the RV version. I'm not all that sure of the difference between them, they seem to look the same. Dometic just makes the trim ring that goes around it too, to make it look built in. In fact, Sunline did use Dometic microwaves back in the '80's, and then they moved to a household brand (like Goldstar or something) during the '90's, and then sometime around 1999 (when they went to the white appliances), they returned to Dometic's.
Here's the picture. It happens to be in an '01 A/L L-19B:
Jon