They should pay. Nazis can never make up for what they did.
The Nazi’s aren’t around to. Thats the problem.
There has got to be a reasonable statute of limitations. For example, Italy should not be expected to pay for excesses committed by the Roman Empire.
But what should the statute of limitations be? It's a judgment call, but there are still Greeks alive today who suffered under the Nazis. And their children are worse off because of it. So I'd argue that in this case the statute of limitations has not run out.
Of course, any money Germany gives to Greece would just be wasted. And it would start a cascade, where have-not nations would make all sorts of claims against the have nations.
One could easily argue that the NATO nations, primarily the USA, paid Greece billions during the cold war. Greece has always been a taker and used its unique geography to get billions in direct and indirect aid. If the money dried up, Greece threaten closer ties with the Soviet Union.