I have had that same issue in my 84 & even after having the leaking
master cylinders replaced, brake & clutch, still have the issue. I
believe that the real source is either a leaking windshield seal which
was kept when a new windshield was installed a number of years ago, or
a leaking antenna seal.  The moisture is only on the drivers side, & I
too have a rubber matt over the carpet, & it appears the moisture
comes in under the matt as the matt is usually dry.

YMMV,

Mr. BZ-brake fluid did eat the paint, but now seems to be ok

On Jun 12, 2010, at 12:22 PM, Don Hanson wrote:

>  From multiple muffed brake and clutch reservoir/MC removals and
> replacements I have brake fluid soaked carpet under my feet.  I have a
> rubber mat that covers the carpet.  Whenever I remove that mat, it
> is wet on
> the  under-side and when I lift the carpet (dark brown now) there is
> plenty
> of moisture in the padding under and the carpet is wet as well.  My
> van is a
> working van not a show piece but I'd kinda feel better if the floor
> wasn't
> wet all the time.  Anyone have any ideas how to get this blotted
> up?  I know
> brake fluid loves H2o, so I am guessing that it helps collect water
> in the
> carpet.  I also live in the Northwest, so I bring wet feet into the
> van
> often.
>
>  Ideas? tricks?
>
>  Don Hanson