Most any parts place will have plastic check valves in stock from Dorman or other manufacturer. I ordered a GM one two weeks ago and thought it had the right fittings but it had 1/2” on one end and 1/4” on the other. Went to my parts house next morning and that what they had as well. I made bushings out of 1/4 hose and the 1/2” hose for snug over that. Replaced them both with those new checks and the shifting and braking works great.
