My 1990 Aerostar has a air leak in the Brake power booster somewere and it is making the van run rough.

I took it off this morning and see that it might be leaking from the seal between it and the master cylinder. This may not be were the air leak is, I am guessing.

Is there a way that I can check the diaphram to see if I need to replace the Booster?

One more note. The Booster has a small amount of brake fluid in it. Is the normal?

 

Ouch. Don't know about the fluid, but check the vacuum line going back to the rear of the engine. Had mine pop off, thought I would have to do the whole booster/master cyl. Ended up being the vacuum line.

 

Fluid in the booster indicates a leak in the master cylinder. That may have caused the leak in the rubber diaphram in the brake booster. At least, you should replace the leaking master cylinder.

There is usually a one way check valve on the vacuum line going to the brake booster, so the vacuum should be held even with the engine off. If you pull the line (engine off), you should hear the air get sucked back into it. Another way to check is to apply the brake pedal a few minutes after the engine is shut off. There should be enough stored vacuum to allow at least two easy pumps of the pedal before it stiffens up.