The only Vikings I have ever dealt with were from the mid 70's.
They were the Chain-D drive models.

With those we just added some 90W gear lube and about 1/2 tube of grease to the gear box.

I believe the Viking tiller line was private label manufactured by Gilson Bros. for Eaton Canada. Both worm gear as well as chain drive Gilsons require EP-140W gear lube. I guess adding grease (what kind?) won't hurt, but that was not a Gilson recommendation.

This unit says chain drive on the cover but it uses a v-belt.
Thanks for the help I will try and find some EP-140W gear lube.