[Vwdiesel] squishy brakes?

[Will Taygan]

I'm wondering if I have a vacuum leak?  94' 1.6TD FrankenJetta
(originally gas).  Pedal sinks if pushed slowly.  Works great if pushed
quickly.  Lots of pumping leads to a nice hard pedal but with very very
little braking power.

Bled rear brakes, no effect (although the right parking brake cable was
stuck on - I've got new cables on order, although i suppose it *could*
be that rebuilt caliper I put on last year)  Front brake bleeders are
stuck/rounded.  Power lock vacuum is working fine.  Couldn't find any
obvious leaks between the vac pump and the brake booster.  I put some
RTV silicone around the grommet at the brake booster, just in case that
might help.

Ideas?

Thanks,

Will in Alaska.

P.S. I'm thinking about just pulling this engine and putting it in the
'82 diesel Westy, but I gotta figure out how much work that actually is
first..  Winter is coming!