Courier bag waterproof "Tizip" problems - not closing. Help?

dm40
dm40 Posts: 5
edited November 2012 in Commuting general
My Ortlieb courier bag isn't happy - more specifically the waterproof Tizip isn't, as recently it hasn't been closing properly and leaving open gaps along its length, exposing the contents to the recent glorious weather!

Anyone experienced any similar problems with these zips?

If so, any tips/tricks that may help to fix it? or is this terminal and is it time to replace? (which is a shame as rest of bag is still great).

In detail: the 2 sides of the zip don't join together with the zipper - sometimes remaining open along the entire zip length, sometimes just 50 % or so. This can be improved by twisting the zipper to one side as pulling/closing but still a bit hit and miss.

So far, have tried re-lubrication and manually trying to join halves but no real improvement and can't find any other info that may help.