I only have S-chassis manuals from '95-'98. But for the '98 500 MXz they call for 2 1/2 turns for a baseline. I would think that '99 and '98 would be the same, I really don't think that 'Doo changed anything between the two years.
It is common on older sleds for the check-valve in the oil lines to stick, slowly draining oil into the case over time. Especially if the oil bottle is full. Running the sled will blow it all out....
