Dear enthusiats,
Just an update to the stiffenning of the brakes on my 99 boxster.
Turns out that water had entered into the master cylinder via the booster. Also found that water had initially collected in an area under the bonnet as the drains were clogged with dried leaves which eventually made its way into the booster and cylinder. Anyhow, after a thousand bucks later, it's all good (costs also included draining the brake fluid and replacing some pads).