Hi,
Firstly Dont Drive your van. Its dangerous with Brakes like that
You need to have them bled or if you can do it yourself you will save money. Its all in the wiki on how to do it. It could be all manner of things really. When was the last time they were flushed flushed with new fluid ?
When was the last time to checked the fluid in the reservoir (Behind the speedo and fuel gauge pod).
You need to check the Servo pipe that runs from the engine right to the front..its usually a pale yellow colour and also check the non return valve. Check all flexi pipes on all 4 corners..ie one to each wheel on the front and one to each trailing arm on the back. Look for leaks,splits and heavy corrosion around the ferrel.
ABOVE ALL DONT TAKE CHANCES WITH BRAKES ! If you are unsure let some one who knows look at them !
As for the header tank bubbling. Im not too clued up on the wasser boxer lump. You need to ascertain if it is overheating and if it is why ?
If it were mine I would be flushing all pipes and the radiator and changing the thermostat for a new one. Also while I was at it I would be changing the sender unit too.
Glenn.
Life is not a rehearsal...Live life to the max....Buy a Aircooled VW and get covered in Rust and Oil.......But we all love it really....!!