The white milky bit is where the two layers of glass and the plastic interlayer are delaminating, this is caused through age. I was a windscreen fitter for 12 years and can honestly say that rebonding an old fronty screen is not really an option as the screen has to be removed and re-fitted. (a process that will almost certainly crack a delaminating screen). You can check if it is a leaking screen by removing the plastic stips you were talking about, (they will carefully prize up), pour fairy liquid around the outside edge of the glass and (providing you have access to one), blowing compressed air from the inside around the edge of the screen. This will blow bubbles where there is a leak.
If you are fully comp insured, take the hit (usually £60 or so excess) and have a new screen fitted
Hope this helps