Anyone worth their money will strip the box and inspect the internals, then tell you what it needs. A fly by night will strip it and replace all the bearings and synchros because they don't know what they're looking at!
The TL4 is actually a very well thought out gearbox. It's the synchro rings for 3rd and 4th gear that let it down. I've replaced loads now. I've even fixed the ones that just needed different oil eh
@tombate911 lol