Draughty uPVC Sliding door

[krembola]

I have a upvc sliding door that opens onto my garden and there has been a draught from it for ages, but i don'y know if it's the rubber seals or the metal locking mechanisms. the design is weird, you slide he door along and push into he frame and then the handle locks it shut and shut cut out the noise and cold, but doesn't.

Where could i get new seals, maybe slightly bigger or new metal locking cups as per the pictures in my Images folder called UPVC?

Thanks[/img]

 

[ajrobb]

It might be worth checking the mortar under the sills. When I lifted the flooring, I could see daylight under the frames.