I think you mean the Steering's "universal joint". Yes this can cause the steering to be dificult to turn, but there are several other things that can also give the problem
1. The Universal Joint on the steering column
2. The Steering Rack
3. The Steering Damper
4. The Ball joints on the Track rod ends
5. The ball joints on the bottom of the shock absorbers.
To test if it is the universal joint on the steering rack, you will have to disconnect the steering column from the steering rack and then see if the both joints on the universal joint are free and not stiff. Cure can be as simple as oiling all the joints or else it is a replacement with another one.
The steering rack can get holes in the gaiters (Rubber bits) which let water in and the grease out, result - rust which make it stiff. Test by jacking the car up at the front, taking off the tie rod ball joints and turning hte steering wheel, should turn nice and freely to full lock both directions. Cure, if it is only a little bit rusty / stiff then new grease put in will improve things, but as long as there are holes in the gaiters, you will allways have trouble. Best cure - new rack
The Steering damper can lose the internal seal and either fill up with water / gunk and become stiff or more likely, lose all the oil inside which means it is not doing its job properly. Test by removing from car and trying to strech and compress it, it should only allow you to do so slowly any sudden actions should result in very little movement.
Ball joints on the track rod ends can develop cuts in the rubber sleeve which allows water in and so rusts the internals. Test, using a ball joint splitter remove the tie rod ends from the ball joints and move the ball joints around by hand. If they do not feel smooth then they need replacing. Do all four (4) and be do with it!
The same for all the other ball joints on the front end. To be honest, they don't cost that much each and even if the old ones don't feel terrible, putting new ones in will make the car feel nicer to drive!
They are only held in by two bolts each and you get those with the kit when you buy it from Smart / MB / Spart Parts Direct / or who ever.
Sorry this is such a long post, just trying to cover all the things which give heavy steering (been there, done that!)