I am thinking you have a 123 - the old style. I have a 123 240D and the valves are real easy to adjust. You don't need the funky expensive bent 14 mm spanners, although they would make the job easier.

Read up on valve adjustments at this site - I'm sure you'll find lots of info. If not, let me know at this thread and I'll email you the job from the workshop manual. Haynes actually tells you how to do it too - you could get one of their books.

If it's a 124, it has hydraulic valves - if one of them has failed, you'll have to buy a new one and put it in - a bit of a job. BUt using Mobil 1 synthetic can help.