I did a write up when I replaced the Hall on my 1985 1.9L here:

http://www.thesamba.com/vw/forum/viewtopic.php?t=524320&highlight=

I don't know what the difference would be for a 2.1 but it is a different
part number.  On the post, Windnsea replied that I did not have to remove
the distributor to replace the Hall, but did not provide any details.  Even
if it were possible, with so many tiny screws that have to be removed I'd
surely drop at least one in an inaccessible place.

On Tue, Oct 1, 2013 at 8:06 AM, Jim Felder <jim.felder@gmail.com> wrote:

> John,
>
> If I recall, pop the distributor cap, remove the rotor and plate and lift
> the sensor out of its slot. Unplug the other end and plug the new one in
> like that one came out. There may be a little more to it than that but not
> much.
>
> Jim
>
>
> On Tue, Oct 1, 2013 at 6:04 AM, JRodgers <jrodgers113@gmail.com> wrote:
>
> > How difficult is it to change out the hall sending unit. Mine is shot,
> > apparently. What has to be done?
> >
> > Thanks,
> >
> > John
> >
>