Ever bought a set of those cheap Chinese-made multimeter probes? They probably had some little plastic inserts in the banana plugs. For what reason I’m not sure, maybe to keep the safety shroud around the plug from deforming. Don’t toss them in the trash. Instead toss the probes in the trash (they’re not that great) and keep the inserts, because you can fix the broken inner jack shrouds on your $300 Fluke DMM with them!
A brand-new jack assembly can be found for $30 (or more), but this is quick and the results are pretty good.
The ‘CA activator’ mentioned above is a very volatile fluid that comes in a spray bottle. When it comes in contact with cyanoacrylate (CA) glue, it causes a chemical reaction that results in instant hardening. The common water-thin variety of CA glue (aka superglue) usually just makes a mess, but the slow-setting gel form of CA glue, used with the activator, can make effective repairs for many non-porous materials. A small bottle of CA activator is not expensive and should be easily found in hobby stores, since CA glues are very popular with airplane modelers that use balsa wood.