Daily drivers "worth buying" ?

It's a hard judgment call of weather to replace an old car/ with another OLD car. Or to dump money into the one you presently own.
With the one you own, you know what's been done to it. Are PT Cruisers known to have head gasket rot/ wear out... like the old 2.2 & 2.5 kcar 4cylinder engines ? If so about what time frame/mileage. That could make my decision also.