I have a 98 Astro. It's loosing brake and steering fluid
with no visible leaks. I'm assuming thebooster is
going.Should anythingelse be checked
first?

***Edit by EuroGoldLS-----Reason: Couldn't read it, increased font size.***

If its losing brake fluid, tighten the bleeder screws. I don't know how you could be losing PS fluid without having a visible leak. Make sure you check every line.