I live on a very steep street, always park downhill.  I haven't had leaks or
any problems that I've noticed.  I always park downhill because I can't
start the van and go up the hill, it's too steep.  In fact I can't even
reliably drive up my street at all.  I always leave it in reverse when
parked (Matilda's a manual), parking brake on as hard as I can get it (if I
don't totally yank it on, she rolls, even when in reverse) and wheels angled
slightly towards the curb.

I'm quite amazed that I can actually parallel park on my street.  It does
sometimes amuse my neighbors to watch, but I've only had problems a couple
of times.

Joy