Many of us have adapted the Mamod point levers to get around this issue. This posting is asking for you to air your solutions so others of us can do the same without having to re-invent the wheel.
I'll start by giving the solution I've adopted. This isn't original to me - I saw it in use on a display at a Garden Rail exhibition and borrowed the idea.

Fully open

Partly closed.

Nearly closed the other way. Just a little more pressure on the steel rod and the points will be fully closed.
What appears to be dirt on the outside of the operating cylinder is in fact grease.
The new points lever consists of a brass rod which rotates inside a brass tube by moving a thin(ish) (stainless) steel rod screwed into the side of the brass rod and projecting through a slot cut into the wall of the brass cylinder. The slot is cut at around 45 degrees so that by moving the steel rod it causes the brass rod to travel backwards and forwards in the cylinder.
Attached to the end of the brass rod is a brass wire shaped as in the photograph, the far end of which attaches through the hole in the end of the Mamod points operating arm.
My points lever has been outside for the last 18 months and works fine. The only maintenance is a blob of grease in the Autumn.
However, what I'd like to do is to operate the points remotely. I've vaguely toyed with a few ways (eg cables, pneumatics) but that's as far as I've got.
Any other contributions or comments welcome.
Mike Wakefield