Shift shaft leaks

Discovered something that may help leaky shifter shafts. Disassembling my dead 87-430 engine, broken LH main case. I'm going to use the 87 clutch cover on my 84-500, after I put a soft plug in the WP hole. I went to put a new o-ring on shift shaft and found it has two, on opposite ends. 84 had only one small diameter one towards outside of case. Easy modification on a chronic leaker with single o-ring. I used universal o-rings out of my Caterpiller o-ring kit. I apologize if this has been discussed before.