As I get my car ready to drive, I noticed, that the cap for the coolant reserve tank is missing. I have looked on the major sites, and have not found one. Is this something I'll have to scrounge from a salvage yard?

Yes boneyard is your friend.

Yeah I was afraid of that, I can look around, or as last resort rig up a homemade cap

I was looking in the trunk, and found one of the caps that was on the water pump outlet that was applied by the recycling yard, I inverted it, and it fit inside the jug perfectly, A hose clamp on the outside, and voila

That won't work for long. The cap needs to breathe well enough to allow air to get in and out as the coolant (and air) expands and contracts with heat and cold.

I did find a Dorman part # 54217 cap, but cutoff fitment year is 1998.

`98 versus `99 should be the same reservoir cap. GM used those on just about everything for a long time.

That'* what I was thinking, I remember those caps on 80'* GM cars too. They want $15 for the cap only, but for less than $10 more, they sell a complete replacement jug, with the cap. I think I'll snoop around my local salvage yards and see if I can snag one first

If they are selling a reservoir with cap for $25.00 , get them. I'm amazed that they make those and I'm guessing they won't much longer. May as well refresh the plastic reservoir while you have a chance. It won't be long before there won't be any of them left to find.

I found the cap, for $4.69 at O'Reilly'*, fits perfectly