If you are going to keep the car I would replace the E.T.M. It will get to the point where the car will not move.As far as the Trans goes you can drive it till it fails but how does the fluid look? If it is a brownish color it may be worth flusing the old fluid out (and any particals that might be plugging the S-1 solenoid)and filling with new.If the fluid is discolored I would have it flushed soon as driving it continually with bad fluid only leads to more problems like writing that $4,500 check.