Evenin' Frank.
Sounds like the buffer pad which locks the quill has dropped a little.
Unscrew the top locking knob and look inside the hole. There should be a small metal pad at the bottom. This has a machined straight section which fits into the slot on the top of the quill. 1/ It stops the quill rotating, 2/ It stops any damage to the quill when you lock it.
Slide your finger into the quill hole and push this pad upwards into the threaded hole, if it slips back down push a small blob of grease into the hole to hold it. Slide the quill back in, when in and threaded on a few threads, rotate the quill while pushing the small pad back down to locate it into the slot on the quill top.
Fit the locking knob back and all should be well. (He says hopefully.)