Thanks @David Johnston. Actually the fingers on my unit are surprisingly soft IMHO. While the unit was labeled c8 as per Stout, I think it had been used since the signs were documented as being repros. So perhaps the sleeves were replaced and the fingers are new and soft, I don't know.
Just today I took delivery of a NOS cart for the 356, but haven't looked at it yet. I will open it up on Tuesday and see how it compares to the ones I currently have. I'm thinking if I can't solve the speed differences, I can have 3 carts on the track, with 2 being in the station and the third one coming into it to release one of the two.