The Bath tub drain is not draining like it should -- very slow -- I think the open/close mechanism is the problem, but don't know how to fix/replace.

You probably have a totally unpleasant hair ball clinging to the stopper. Try to remove the stopper or fish out the junk with a wire. Pour some drain cleaner in it and allow to sit before flushing with hot water. Try a 1/2 cup of salt mixed with 1/2 cup baking soda. Dump into the drain and then add a cup of vinegar. Allow to stand over night and then flush with water.