RV Repair: 1981 winnebago, working with copper, water leaks

Question
I have several water leaks in the fresh water system. These so far have been from 1/2" gray plastic flare nuts cracking. which  secures gray 3/8" tubing.
Can you still get parts tubing fittings?  or should it be replaced with something newer?  Due to age should I replace it all? Do you use a flare tool on this tubing like working with copper?

Answer
I know it is a pain, but I would replace with all CPVC or drinking water tubing.  If you decide to just fix the connectors, go to Home Depot, down the tubing isle.  You will see many options.  I would change this because over the last 30 years, there are many quality improvements in material.