Locate hole; scuff rubber; apply rubber solution; cut circular patch; let rubber solution go "hazy"; apply and press patch; talc to finish off.
Those that didn't leak immediately would last a day or two.
Then I started fixing car inner tubes (in the days when they had them). No better. Despite my Dad having a machine to heat and seal the repair. (And his repairs never lasted, either).
Last week SWMBO wheelchair (****ing thing) sprang a leak. I went for my *brand new* spare inner tube to discover the ****ing thing had a split.
Of course no cycle shop actually stocks these tubes (despite what any website tells you). So I took it to a local bike shop for *them* to repair.
You can see where this is going, can't you ?
In their defence, they advised a new tube too, and we are talking 140 psi.