Hey Quijoteos, I know what you mean man!

Over time, the wiper motor gets slower and slower.

A lot of the performance of the wiper is influenced by bad power connections to the wiper motor. The wiper needs a good healthy 12v feed and a good thick earth.

The 1200 loom is almost not up to the job.

First trace the wires that go to the wiper, and ensure the connector terminals are all clean.

Pull the wiper motor out and disassemble it. Clean out all of the dirt using metholated spirits. Using 'wet and dry' paper, smooth the commutator surfaces, and check the condition of the brushes.
Regrease the motor bearings and reassemble.
Make sure the gears are all well greased also.