Do they go sideways of are they just "heavy" to lift? I have some cellular blinds and some wood minis, that I have replaced the pull cords on a number of times. This type of surgery for a cellular blind in pretty hard, a mini blind is much easier as you can feed the cord through all of the openings. This may the answer to your problem as well. I get about 5-6 years of near daily use before the string frays a bit and they begin to get troublesome. When lifting them I tend to grab the middle and lift while I'm pulling on the cord this helps a ton in the longevity dept.
Everything is in working order,except for the gap when I close them shut.
the gap at the bottom?...or the gap when they are "rotated" to block the light?
The gap at the bottom is fixed thing based on the overall length of the blinds. I most cases I have set these up from "longer" sets and then shorten to fit. if these are too short there is no way to make them longer.
It's the gap when they're rotated to block the light. Having the light in, during the day is 'blinding" (pun intended...) Sun comes in the windows,from the West. The lamp post, shines in too night time. To close and open them has become a pain, morse code!
If you cannot rotate them to look up instead of down, There is nothing you can do to prevent the light from coming in at an angle.
Some blinds work better then others at blocking light when they are rotated closed. Not knowing the quality of blind it is that you have, there is little advice one can provide other then rotating them the other way so the angle is reverse what you would normally do when you close them.
Also....has this always been the case or is this a new phenomenon. If these have never worked well then it may just be poor engineering on the manufacturers part...which is common in lower quality stuff.
It may be time for an upgrade to new
This is a recent phenomenon. The (custom metal blinds) work well in every situation (glide turning the wond... and the quality is wonderful...made in the USA}
If they were made with vinyl or plastic, I'd recycle them long ago.
My windows are big and the sills are shallow, hard finding other options to work with. Unless I'm looking with my eyes closed Lol !
Then is sounds as though something is binding them. If it worked well in the past, something is not allowing them to rotate far enough to work properly. Check on the top to see if you can view the hardware that does the work. perhaps something is stuck in the gears that make the blinds rotate.
On my cellular blinds one of the early stages of "fail" is a frayed cord. when worn like that it tends to bind in the slide mechanism. Your blinds may be doing the same thing...check at the top were the front and back guide cords come out of the header.