You probably have the nice but useless version...
Try these ones: http://www.minispare...|Back to search
Check the arms are the same too as you might have to change them at the same time...
Ps: have a look at 'I love Minispares!' tread in 'mini chat'
Just been to have a look, and mine are made by Tex, I don't know if cheap type or not, though they look good quality? I went to your link, and they mention my wiper motor and wheelboxes must also be in good condition, how would I know, and what is a wheel box? The current wipers do move enthusiastically, though without much pressure on screen.
It's the part your Wipers attach to and swivels, it gets bunged up with crap and should be taken apart to help relieve strain on the wiper engine along with the cable, tube and of corse the engine mechanism. Then greased.
Every 10 years or so...
Not sure the boxes actually come apart but a good clean and grease should suffice.
This way all of the force of the engine will go to the blades and you can put more downforce to the arms by bending or putting a stronger spring on.