oil in water and hoses bursting...HELP!

[mamn97@dial.pipex.com]

I've just flushed the cooling system again and refilled only to find 
more mayo forming in the water and the seal on the reservoir cap 
now broken (high pressure?) Have been told by a guy at halfords 
(crap car place in U.K.) that it won't be the head gasket because 
there is no water in the oil and no white smoke is seen from the 
exhaust.  (I can't do a pressure test as havnt the equipmnt)  

Have thought...... could oil getting into the water be caused by a 
blockage in the cooling system??........ my brother says not but i'm 
not so sure...... when the T shaped pipe burst (£40 ukp!) I found a 
piece of grey plastic which looked like it was off a join which had 
broken off somewhere in the system. I only found half of the thing 
so am guessing there is another half somewhere??? could this be 
the case?  Have taken all teh hoses off once to have a look but 
can't find anything - am thiinking though that it may be somewhere 
in the block?? Am also wondering where the plastic has come from 
and if it is important??? 
I am sure there is some reason behind 3 of the hoses busting and 
maybe even the fact that the bloke I bought it off had to replace the 
oil cooler and radiator.
TIA
Rob Shiers 
(getting increasingly frustrated!!:( )
jetta 16v
80 sport