My fluid trainer lost most of its resistance after about a year, but that was because the fluid had leaked out. I contacted the manufacturer and they had me send the resistance unit back to the factory and they sent me a new one (or perhaps a refurbished one). $5 or $6 to mail it back was all I paid since it was still under warranty.

Your unit sounds like it has a different problem but maybe it's still under warranty and you can get it replaced.