Incidently I think I did read a thread on the operations of these DT banks and I'm sure someone said that when the round rod at the bottom of the bank gets a bit of wear in it ie: when a groove starts to get worn into the rod after 1000's of operations this can affect how easy or hard it gets for the target to drop down. Might be worth thinking about getting a new rod if the old ones a bit worn.

I wonder how much use a manchine has to have had before this happens?
I have only taken apart two of the drops so far, apart from a little wear on the metal arm that attaches to the target, the drops are in very nice condition, all they are needing is a really good clean