Need some help with an International 8600

I have a few random problems with a company truck that seems like the mechanics can't or don't care about fixing. I was wondering if a few of you could chime in if you know what may be going on so I can fix it myself.

1 I think the blend door is or has gone bad. Air only comes out of vents and not defrost of floor. What's the easiest way to check or replace or just slap it a few times?

2 it spits and spudders slot with random on and off engine light. I believe they said they cleaned the EGR(or similar diesel part) once then may cleaned again or replaced second time but its back to doing it again.

3 are the lights for the gauges in the dash bulbs or LEDs? I have some out and was told its time consuming to replace.

4 the headlights I've tried to aim myself on the side of the road after they just torqued them to the sky. But I still can't see anything. The haze has been cleaned off so there clear, I put new xtra vision 9007 in, but still not much difference from low to high beams.

5 what's the secret to get the drivers door to stop whistling in my ear? I put some foam strips along doors edge which worked great but water started leaking in so I had to remove it.

Thanks for any help, really appreciate the help!