Windscreen washer 'soap'

Is it ok to put any sorts into my car or do I need to buy a certain type?
I did not have to add any treatment for nearly 3 years as the suds just kept coming from the original MB fill.
I do think that it is best not to use anything ( if you can get away with it) as any cleaner will remove the wax from your paintwork therefore exposing it to oxidisation.
How is the new car going ?





