not a big job but can be fiddly.
theres a few threads on this.
http://www.fbekholden.com/forum/viewtopic.php?t=438
http://www.fbekholden.com/forum/viewtopic.php?t=3366
you can get the rubbers form rares or spectrum.
some people take the whole 1/4 out and to do this you have to remove all the door guts - glass, winders etc.
or some people make a small cut in the rubber and glue straight in.
if you take the whole 1/4 out be careful not to snap the shaft at the bottom when removing the bolt as its usually rusted in.
Stewart