Driving along in the old 300SL Benz the other day I got caught out in a typical QLD monsoonal rain shower that was pretty short and heavy. It became quite dangerous as the wipers were not working at their very best (even for 1955 wipers they should be doing a lot better), leaving long streaking marks across the screen, making it very hard to see!  After the rain had passed (just 1 minute later), I hopped out and had a close look at the wipers and glass. The blades were new, so I looked at the wiper arms - they were giving enough pressure for the blades to be working on the screen, so it was then down to a close inspection of the glass. It had a lot of different materials bonded to the glass surface, which would have been from the many happy years of driving (and racing) it has given us. These minute items on the glass were causing the wipers to not be perfectly flush with the screen and helping create the issue of not being able to see safely in the rain.