Your 72 MHz gold stickered Tx/RX systems are still legal. In fact, at most fields 2.4GHz popularity has freed up the 72MHz frequency board. If you have some stuck or tight glow engines they can be freed up by heating them with your covering heat gun then adding some after run oil when they break free. Same for stuck carb barrels. After freeing the engine fire it up and run a tank thru it, and then give it after run oil before storing it. As for the batteries, replacing all of them would be a 100% sure way to be safe. Depending on how many systems you have this may be rather expensive, however so is crashing your planes because a battery failed! If you have a good battery cycler such as the Hobbico Accu Cycle, then I would give each one a go on the cycler and see how they do. Load test them afterwards and retest them after a week or so. If in doubt, throw them out. It becomes a "judgement" call on whether to use them or go the 100% replacement route.