replace/substitute 8" bextrene woofer?

I have a pair of Tangent Acoustics RS4 (built around 1980) speakers with Audax bextrene 8" midbass woofers. I've just noticed that one of the woofers probably needs replacement. (I noticed that blown-woofer-buzz on a stand up bass solo, but not too noticeable on any other track so far.) The trouble is that Audax doesn't seem to make that driver any longer. I know nothing about speaker engineering. What can of worms am I opening if I put another driver in there? I assume I'd have to replace both. The bextrene drivers are very inefficient (84-86), and with new drivers I assume these would become very different speakers. What are my options? How would new, more efficient drivers match with my tweeters (Audax, I think, 1" soft dome)? Crossovers, etc? Or should I just live with it (avoid bass solos) until I can afford new speakers? I understand that speaker technology has really improved since 1980 anyway.