I have a 77 II that had this issue and found that carefully removing the zebra strips and gently wiping the ends and contacts with an alcohol (denatured) soaked paper towel fixed it nicely. Replacement strips are sold on eBay but I decided that it was worth trying to clean the existing ones, safe in the knowledge that if I damaged them I could get new ones. For all I know, simply breaking and remaking the connections may have done it, but cleaned things since it was apart.
Do a YouTube search on cleaning fluke zebra strips or stripes, and you'll find videos showing it. It is quite simple, and in my case at least, worked perfectly.
-Pat