They do have a finite life - most come with instructions to replace them every five years or so - but in reality they tend to last about twice that long. Same with the CO2 detectors. I'd replace it. Why take the chance?
Any name-brand RV propane detector will do the trick, unless yours is one that also turns off the gas when it alarms (mine does). When my detector started not detecting leaks after about 10 years, I found a guy who could rebuild it. I have it tested every year and it's all good. Not looking forward to the next time it dies - there are no direct replacements available.
al