Are you sure all the steering components are tight? Check the linkage first with special attention to the tie rod ends, idler arm, etc. I can't picture this steering system in my head at the moment but I remember it being a pretty standard deal similar to many American cars of the era.

After you tighten up the steering linkage parts you can proceed to the steering box if needed. There's an adjustment screw but you have to be careful as you can overdo it - it'll be worn more in the centered position than at the ends of its travel so if you make it too tight in the center it'll bind at the extremes of its travel. If it's TOO worn you'll need a rebuilt box but its too early to know that yet. Tom has given you good guidance in the particulars.

Let me add a caution here - DO NOT go cheap on steering components! If you look on any of the on-line parts sites (I haven't checked Pelican for your particular car) you'll find parts at a whole variety of prices. I'm not suggesting that you can only use Mercedes-brand parts (though they'll be top-notch) but you don't want cheapo Asian-made stuff either. The cheap stuff simply won't hold up.

Dan