A 25 year old A/C evaporator is a nasty thing to look at - imagine, all the cabin air I was breathing passed through this thing for years. here is how I replaced mine. http://mgodfrey3.blogspot.com/2011/12/1986-toyota-celica-gts-ac-evaporator.html
Yes - the evap was beyond cleaning and since I had it out I relaxed it and the txv as well as the o rings. The evap was only $50 and the txv was $25.