Go to your nearest Pick&Pay, go to the isle where they sell plastic items and look for that typical square white plastic water bottle. Drill a hole in the cap to accommodate the plastic tubing and ......voila .... you have a windscreen water bottle at 1% of the price from MB!:-o
I fix mine also quite regularly but I use Q-bond after I file a clean vee through the crack. I am now thinking about using some type of adhesive from the inside - like allowing paint to dry in the tin and causing a liner in there. Bostik or stone chip or bitumen or.......
Someone IIRC used the wheel arch moldings from a 463 and fitted them.
To be honest I don't think too many of the bottles are broken from stones but rather ond age and brittle nipples the pipes go on and tabs breakig off.