La Crosse 90 bottle levers stick in "up" posiion

[Marketblandings]

My '64 La Crosse LC (ILL) 90 9 has worked in almost every way since I first got it. A real hit at parties!
However, sometimes the roller-levers (sorry. Don't know the real word!)  that allow the bottles to pull out get stuck in the "up" position. This keeps any more bottles from vending, of course. The top 4 bottle holes mostly. The lower holes are much better. A flick of a finger fixes it - but my guests don't know to do that.
I put in a refurbished Mars coin-mech last year (for other reasons) and this problem surprised me by going away for months! Now I am back to sticky levers now and then.
It seems like a lube problem - but the business end of the roller levers is buried under several plates of metal. I can't even SEE where lubrication might go.

Help appreciated!