My wipers will park but not cycle back and forth. This is a rebuilt wiper motor that was tested before it was shipped to me.I removed the main valve spool which is spring assisted and found the spring does not fully shift the spool.It appears that hydraulic pressure is supposed to assist the spring to fully shift the spool but is not. There is sufficient pressure to turn the steering wheel with one finger and the wipers park if moved out of position before the engine is started. I made a spacer to stiffen the spring to ensure the spool fully shifts but this did not help. Any insight, suggestions or references would be greatly appreciated.