I did this on an old Advent last year (Think it was a 6417, 1Ghz) and it was an absolute nightmare

(I can solder and have done detailed PCB work before)
The link above for the zx5000 looks a lot lot easier than the Advent one I had to do, it had to come completely to bits (internal shell too and it was none too accessible)
Took about an hour to safely dismantle it, about 20 minutes to sort the socket (tiny annoying multilayered PCB, have to be really careful!) , and about 40 minutes or so to put back together.
It was only the second laptop I have dismantled and repaired though (the first being quite a few years ago, and that was a very eldery Pentium 90 (

) based Compaq)