After replacing most of the worn shift linkage components (see • Transmission shift lin... ), the turbohydromatic 350 automatic transmission in my 1974 Chevrolet Monte Carlo still had some slack in the gear selector and weakness in the detent "click". Since all the linkage had been gone through, the issue had to be inside the transmission.
The TH350 detent spring assembly (GM # 6260153) and the shifter rooster gear selector lever (GM # 330136) are made of "unobtainium" (discontinued long ago) and were sourced from eBay. I got the filter kit and transmission fluid from the local parts store.