Leak around sliding glass door

I have a small outside air leak I want to fix at the base of one of my sliding glass doors. The door slides (closes) into the weatherstripping of the frame properly at the top and middle, but I can see a sliver of light and feel the air coming in at the bottom. Maybe 4 inches. Do sliding glass doors have any kind of adjustment so I can get a more uniform fit with the frame where it seals? I'm thinking not but thought I'd ask.

Is there anything else to try? I don't think I can fit any different weatherstripping into the door. The weatherstripping is OK, the door just doesn't slide into it all the way to seal out the air leak.

At the bottom of each ouside frame edge the should be a hole you can insert a screwdriver ( usually phillips ) into and raise or lower the rollers. If they are really old you may need to remove the slider and replace the rollers from the bottom.

removeable caulk sold in tubes like regular caulk

Right now I have a rolled up towel on mine.

Houses settle. That's a fact but I believe it's a good idea to investigate any time you notice a change like this in a door. It's probably nothing but it sure wouldn't hurt to examine your door sill and make sure that you don't have rot starting in that area. As Nshif said adjusting the rollers will likely take care of the gap.

I have two screws near the bottom of the sliding glass door. I'm hoping one of these is the adjustment screw. I'm worried the one I turn might be screw holding things together and it either comes loose or falls apart. I've never had the door off to investigate the rollers up underneath.

You should be able to lift the door up and remove the bottom from the track then slide the top out . put it on its side and look from the bottom and you should be able to see the rollers. This should tell you if A) one is worn out or B) which screw will adjust it up or down

See if this helps any you should be looking for a hole to insert the screwdriver into not exposed screws as those are probably holding the frame together

http://www.prime-line-products.com/howtoslide3.asp