If you go to plastic twine, better in my opinion, you'll have to tighten the twine discs down pretty tight because the plastic is sicker than what you have. We had a lot of trouble out here years ago when plastic first came out. Then they found some cheaper stuff that really caused a lot of grief. It was white with a line through it. Worked ok after everything was tightened down real good. If the tension plates are wore with a grove you can build them up with brass or weld them over. Just make sure they are super smooth when you put them back on so you don't burr the twine.
Happy Haying