Trico is now own by Stant Corp. Their website is down for now...for how long...
Here a link to service & repair of UK version that from railcar manual:http://www.railcar.co.uk/mechanical/wipers/trico/service.htm
Have you been to NAPA nearest store? They have heavy duty truck catalog to locate your parts if it still available.
Rome Truck advertise air wiper parts. Their requesting site is out of order for now???
I sent a e-mail in regard a online catalog or whatever available to obtain air control valve & motor parts.
Sojourn for Christ, Jerry