No wipers on high speed

I have searched but not found my answer. I have an 01. Last winter the wiper motor shaft corroded so much the motor would turn so slow the wipers moved slower and slower until they finally seized. The motor overheated and I had smoke rise out of the motor. I removed the motor, stripped it down, freed up the shaft and greased everything up. When I fitted it back in and tested it I had wipers again but only on intermittant and low speed (both these settings the wipers would return to park). The problem is when I switch to high speed I get nothing, in fact the motor will stop working exactly where it is. When I switch back to low speed the motor works as normal. I need this issue fixed for my annual inspection. I figure I may have killed the motor when it seized and overheated. But if so why does it work on low speed. Before the overheating issue everything was OK with all wiper speeds.