I had the same problem as you described, leaking caliper, started pulling to one side.
What I found was the fluid had saturated and swelled up the pad material on one of the pads, and I wasn't getting good braking power on the leaky side.
The one affected pad was swollen in the center, and you could tell that it wasn't gripping (engaging on the rotor) the same as the other three.
The leak was on my drivers side caliper, and the car would pull to the passenger side.
I was told that you can soak the pads in brake cleaner (and/or water) and get the fluid out, and then re-bed in the pads. I had a new set of Porterfield R4S pads, but I didn't try it.
Rocky
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.