we have front rotors and rear drums. brakes are acting crazy; unreliable - or too agressive - or not at all - VERY stiff etc. someome told us it needs a proportional valve. true ? if so - where to get 1 reasonably (none on ebay) also: it is said this olds model shares the same platform with buick & eldorado. true? if so - would they have the same proportional valve ? oh btw; we are parting out a 1969 4drs 98 'lotstaparts' ebay item #4545238719