I have a Lincoln Town Car (1994) which has developed a steering
problem.  When turning the steering wheel to the left (particularly at
low speeds) it seems that the power assistance to the steering is
reduced or even none existant.  This happens irrespective of the angle
of the actual wheels on the ground - movement to the left from any
angle seems to lack power assistance.
Turning the steering wheel to the right works fine and is power
assisted as normal.

If anyone has experience of this problem, or knows what the problem is
- I'd welcome any advice as to the cause.

regards
Martyn