Clean and lube the gears on the ends of the axle shaft - the ratchet is stuck. Depending on when it was made it might have a clutch assembly on each side made into the aluminim-case wheel adjuster, with a grease fitting on each - use a grease gun on these with #1 1/2 White Lithium grease, 1 or 2 shots only. The axle end gears have the ratchets inside the assembly, and you may find a hole in the end of the axle for grease. I use spray lithium grease for these because it cleans the grit out as it lubes. If no hole in the axle just try to spray it in at the back edge of the gear.

saxman - Thanks for your help. Sorry to say that does not appear to be the problem. The right-side gear is not frozen, the gear and wheel turn freely, just don't seem to hook up with the drive gear when I push the handle forward. The left side goes like blazes. Thanks again - MV

Sax is guiding you in the right direction. It may be that the spring is so packed w/ anti-sieze that it isn't able to push the pawl up into the gear or that the gear is reversed. I'm not sure what 'looked like it fell off" means.

Tomplum - "looked like it fell off" means when I removed the right side wheel, there was no washer or clip on that side. Since I never looked inside before, I had no basis for comparison. I now have replaced those with new ones from Toro. No dice. I followed Saxman's advice and cleaned up the ratchet on both sides and still no dice. I'm now thinking that the pawl my be gone too. I can see the spring clearly but it does not appear to be pushing anything.
Also, what may be a dumb question about the gear...it should read R on the right side, correct? I.e., the R should be facing out and not in toward the mower.

Thanks for your help. Guess I'll go back to the Toro site and study the diagram some more. Thanks again - MV