Impossible! unless you have a cracked head near the seal, but that is no
very probable... your leak may come from the water pump (like someone else
mention)... i would also suggest the oil cooler or related hoses:
http://www.benplace.com/engine/water_pump_step56.jpg
http://www.benplace.com/engine/cleaning_pump.jpg

Even with some amount of coolant into the engine oil, oil would be
predominant from a pushrod seal leak...

If i understand, it' comming from the head side??? and not the engine core
side!!! so, i would suspect the head gasket.... (sorry) a coolant leak from
under the head is more dificult to see... take your nail and put it in the
head gasket, fist it need to me soft, second, it may leak a bit when playing
with this one....

On this picture:
http://www.benplace.com/roadhaus/100_0135.jpg

You see the head gasket leaking....but it's not when the engine is not
running!!! if you look carefully, the gasket in in the center (about) of the
pushrods tube, where is your leak exactly????? This is a driver side picture!

A small head crack could also be a possibility!!!

As to your question, a collapsable pushrod tube is a easy job....
Here is a shot (first pushrod tube)
http://www.benplace.com/roadhaus/100_0138.jpg

Cheers, Ben
http://www.benplace.com/vw2.htm