There are lots of available materials for roof repair. Check out eternabond and DICOR products (patch kits & sealants). Although your RV is old and a rubber roof will eventually need replacement, you should also be skeptical if that advice came from an RV service department. Get some advice from a seasoned RVer who has some handy-man skills.
I am a professional roofer by trade and we use Eternabond to repair roofs that are out of warranty all the time. Fantastic stuff. Just make sure to get the bonding surface as clean as possible and use something to roll the eternabond down. We use a silicone roller. Anything similar should work.