MJ - Here's a whole 1987 175 Yamaha parts motor in Beford, MA. The auction is ending in 2 days.
http://cgi.ebay.com/ebaymotors/YAMAH...QQcmdZViewItem
Did you try bleeding the system again?
To get the air out . . . Tilt the motor down all the way . . . loosen the relief screw a few turns. Have one of you kids put pressure on the lower unit while your trying to tilt the motor up. The cylinder should fart out some air bubbles/fluid (out the relief valve) When it starts to lift them off the ground and stops farting air bubbles tighten the relief valve. Continue to tilt until the reservoir sounds like it running dry . . . then stop put more fluid in the reservoir and continue to tilt the motor all the way up.