that is very similar to the trans that the 14sb uses I can see that it uses a much larger spring to return the lever than the 14sb. I would start by disconnecting the cable from the lever and manually move the lever to see if it returns more quickly. if not then you will need to open the trans and clean out the old grease and re-lube everything. if it does return quickly then the cable will need replaced. The 14sb the trans tilts up when the engagement lever is pulled and when the level is released the trans tips down helping to disengage the lever so it uses a much smaller spring. In your video it appears the trans is fixed in place and uses the larger spring to pull the lever back to its neutral position. I found a manual on line for the 14sb that covers all the transmissions that might help you pm me and ill send the link to you its a very large file and has no hyper links do you have to page through it until you find the transmission section but it might help you with disassembly. you can also look up my trans rebuild that I posted on here they are quite in depth but are on the 5spd the 3 speed from what I can tell uses as pacer on the shaft in place of 2 of the gears
https://www.mytractorforum.com/155-...5-john-deere-14sb-5-speed-trans-overhaul.html
https://www.mytractorforum.com/155-...5-john-deere-14sb-5-speed-trans-overhaul.html