Mr. Bob, BTDT!!
If you need it, there are very inexpensive borescopes now that plug into your smartphone and fit in a small (1/4 inch) hole. they have lights at the end and you can stick it in a small opening and see what's there on the phone's screen. This one is under $10.
https://www.ebay.com/itm/Endoscope-5...ss!22576!US!-1