Any way to handle replacement of unknown value components
Reverse-engineering the circuit is a potential step. Look the traces and for identifiable ICs and reference designs of said ICs to see if you can find a similar topology on your PCB. If you know the application of your circuit and can determine the function of the components, then it's possible to determine how sensitive the circuit will be to the component value.

Naturally, this isn't particularly easy for us without access to the actual PCB and some diagnostic tools, etc.