as others have said the best way is a proper fix but......
i have used this very successfully on my old mini when a core plug was leaking (2 yrs+), head gasket leak on my previous fronty - kept it going until i could afford a replacement cylinder head (6 mths+) and my current one which had a leaky heater matrix (fingers crossed no problems for 2 years BUT the heater aint great, guess its probably clogged up with the stuff somewhere??)
theoretically none of this stuff should work, it isnt the right thing to do to add a chemical solution to a system that wasnt designed for it BUT
the question you need to answer;
do i want to spend the dosh getting it repaired? if not try this product.....
