>I have a leaky pushrod tube (was hit by something, got a blow, is
>cracked in the middle).

You could try cleaning with brake cleaner then use JB weld, but a
better repair is:

Get a collapsible (spring loaded) pushrod tube from one of the online
VW parts vendors.

You can replace the pushrod tube without removing the head.

You will have to remove the rocker arm and pushrod, but it's a pretty
easy repair, just rip out the old tube by bending/squeezing it in the
middle with vicegrips then replace with the new collapsible unit.
Use new seals on the ends.

Don't forget to install the factory tin under the pushrod tubes when
you're done...that will protect others from breaking.  If you have
lost the tin, used tin is available from many sources.