Power steering leak

For the record, I did make a donation of $5.00 bucks.

Okay, I have a Mercury Sable, It's a 1990 model, 3.0 liter engine. The dang thang is thirsty for power steering fluid and it makes a mess everywhere I park it. It goes though a bottle of fluid every two or three days. And we've had 2 used power steering pumps put on it over the last two years.

I need to know:

a. Will putting on a new or rebuilt power steering pump fix the problem or are there other possible causes?

b. How hard is it to put on a pump?

I have basic tools. Thanks a lot for your help. You really got me out of a jam the last time.