This little light bulb is NOT available at big box stores (not even IKEA). So Appliance Part Pros is super useful. The bulbs were here in 1 day!
There were 2 parts that matched my microwave, so I bought them both in case one didn't fit (it ended up being part number AP4512653)
Anyway, because the old light bulb broke in the socket, I had to do a fair bit of disassembling (I took off the bottom panel, disconnected some leads, unscrewed the light socket itself, then gently removed the old light bulb screw...it was easier than it sounds...all you need is a screwdriver and some guts! oh...and make sure your microwave is getting no power!).
Anyway, great service!