The Horse Show
S3:E14
1978
IMDb
Shirley rescues a horse from a glue factory and put it in her bedroom. The girls try to find a new home for Buttercup before she's turned into glue. In the end it's Lenny and Squiggy who save the day by finding a farm with a nice pasture who's willing to let the horse live out the remainder of its days in contentment.