If your Rans Screamer is starting to show its age replacing parts for a specialized bicycle like yours makes economical sense. Hubs, bottom brackets, headset, seat cushions, pedals are all part of the parts that wear. Generally all can be replaced relatively cheaply. I bought a Ryan Vanguard that had been ridden to total wear out. The hubs were shot as was the seat back. I was able to replace the hubs and seat back, had a cushion made for the seat. Along the way I upgraded the original 9 speed hub to a 10speed hub with index shifting. New 10 speed rear derailleur. All new wires and cables. Bike runs great and I'm diligently trying to wear all the new stuff out. The bike cost $350 and all the new parts added about $400 more to the cost. I've had the bike for 6 years and it rides great. However I do all my own mechanical work including building wheels. This really cuts costs. If you don't want to do that then costs will be higher for a mechanic to do upgrades and replacements on your bike. I also ride upright bikes and switch back and forth almost on a daily basis from recumbent to diamond frame and back. I use my recumbent on longer rides because of comfort. My diamond frames on shorter rides because of gravel rides and because I love diamond frame bikes too. My wife and I gave up on both recumbent and upright tandems years ago. I'm too tall for any but a custom tandem to fit me. However recently my wife bought a RAD e-bike. Hers is a City step through frame. This has been a revelation to both of us. She is again able to keep up with me for quite long rides and we have been enjoying riding together once again. Good luck in finding the solution to your tandem issue.