O.o
I'm missing the 5th key for the left hand thumb 0.0
I have a semi-solo in one part, and i need an alternate fingering or anything of that sort for the high D

Good luck on that one, mate.

When you're flicking, if you don't have the 5th key, you can use the C (4th) key. Would it be the same for playing that?

Lots of bassoons (mostly older instruments i think) don't have that top D speaker key. Shouldn't hinder you too much though - a lot of the time i forget to put mine down anyway.

My suggestion is to use the normal fingering, but use lots and lots of abdominal support. Which you should be doing anyway :p

As Ruth says a lot is down to breath support; also having a suitable reed helps - i.e. not too soft. The crook/bocal (Which side of the Atlantic are you?) can affect the ability to hit high notes - it's probably worth trying various ones. There is a fairly recently retired London pro player who survived his entire career without a high D key - I wonder how many times he played Rite of Spring without any trouble?

Ian

On my bassoon the high D key tends to be airy anyway.

I just try to remember what I play for D4.

IIRC it's the first two finger holes E,D and Eb (the upper pinky finger key on the left hand)

It sounds a lot opener and cleaner, so I wouldn't miss that high D key and tuning works ok for MY bassoon, your mileage might vary.

There are other alternate fingerings you might want to consider from sites such as thisone :

http://www.wfg.woodwind.org/bassoon/

Cheers
James