try to use one buffer exclusively only for the workerpool, the worker will place his part there and after the break the worker needs to find this part there
the buffer is not the problem;
you are triggering transports by the worker, where the destination is still occupied; so the worker cannot place the parts...
You need to program exit controls (front) where you wait until the next stop is empty; you should also lock the exit of the source, if you transport the parts to station
--> see exit controls