Flat repair/corner sidewall

Have some pics?

 

If the puncture is in the tread face it’s repairable, not the sidewall. Shops on the road are more than willing to move that demark and 1/8” or so if there’s a new tire sale in the balance. Same story forever, they never have a used one or a cap in stock in that size, but they always seem to have one that size with the sticker still on it.

 

If the mechanic/tech told you- likely not in a safe to repair spot and not worth the potential liability. Mechanics/techs will usually get paid more by performing the repair than a tire swap. If it was a sales guy then it's 50/50. Generally you have to keep in mind where the tires flex when in motion. Usually the section BETWEEN each outter channel is safe. Outside that towards each sidewall sees the most flex and heat transfer increasing the risk of a failed repair.

 

You could try doing a section repair which is a plug and a patch.

 

If it has lots of tread left I might try a plug kit and a patch on the inside. But good luck getting a tire shop to do it. Liability problem. A patch or plug on the sidewall gets to much movement from tire flex and often won't hold

 

If the whole is inside the first tread groove then it is not repairable. Anything you put there be it a patch or plug will flex and come out