The stock radiator was a metal core with plastic end tanks. These end tanks would leak at the seam with the core and sometimes the hose barbs would crack or break. Aftermarket radiators are available with both metal tanks and plastic end tanks.
Pleastic End Tank Repair: A radiator shop in Tennessee called Tanks and Tabs sells the side plastic tanks cheap. For the XR they cost $15-$25 and they come with a new o ring seal. I don't have the number but it can easily be found if you call information and search in the Tennessee 1-800 directory. To this day I've never had any problems with the plastic tank that I purchase from them.
Rubber Top Mounts:
Use the Volvo 1228599-5 rubber cushion, fuel pump mount from 80's 240. They are about $5, you need 2
New Aftermarket Radiator:
Well-Built Radiator Mfg. Corp.
Gardena, CA 90248
1-800-540-=1111 (outside L.A.)