http://www.gahh.com
New horsehair is the way to go... I bought a pair of them for the two front seats in my 300SD for a little more than $100 a pop, worht every penny. I also replaced the box springs with a pair I pulled out of a '91 300SEL, since the junkyard I go to only charges $35 for a complete front seat. If you replace the springs, make sure you find the later version with the reinforcing straps and extra cross-bracing.