Lost 1st gear and reverse (gear issues)

[Manu]

Hi guys, just to start im gonna say my English is not the best as its a second language.

Basically, a few weeks ago, out of nowhere, when I went to shift into 1st gear it didn't go forward, and same with reverse, I wasn't home and sent it to the mechanic. He told me it was a teflon piece in (or near, cant remember) the transmission. He replaced it and it works, but kinda doesn't. Sometimes it still doesn't shift and i have to try multiple times and also, the shift knob springs back up when I put it in reverse, but doesn't pop out of gear.

I was wondering :
- Is this normal age issues
-Can I fix it by adjusting the linkage
-What part could he be referring to, and can you find me the details so I can make a new one