South Africa uses Olifant tank.
It’s an upgraded version of Centurion tank. When neighboring countries only have old Russian tanks, it might be enough.
South Korea has some 800 of M48 tanks, upgraded with their own 105mm gun and fire control system.
They do have about 2000 modern K1 and K2 tanks.
They know M48 isn’t strong enough. But If North Korea attacks with 4000 old Russian tanks (or local variations), South Korean modern tanks would be outnumbered 4 to 2. If they add 800 M48s, they would be close to 4:3.
That’s why 70 year old tanks are still used with upgraded guns and fire control system.