I recommend a very lightly dampend rag with liquid dishwashing soap/water mix or saddle soap to get the bugs off leather. Then go over it with Neatsfoot oil. Same stuff I use on the saddles/bridles. I have a leather breast collar on display that my horse I had about 35 years ago that is still in good shape and actually usable. I have been reading on the net that Neatsfoot oil compounds is the one you do not want as it is petroleum based. But the two shown in the links here should work just fine as they aren't petroleum based. Saddle soap is also good by some people but others don't think its good. I have used saddle soap and neatsfoot oil for many years on my horse leathers and use it now for biker leathers. Here's a good article on how to clean saddle leathers that basically say what I said.