Replaced the brake booster servo (got a used one from
this UK shop, and it was MINT/NEW condition). What can I say... the previous owner of the car never knew the joy of life! He was struggling with a sticky ON/OFF type of brake pedal, and a new one feels sooo much different. If your brake pedal feels heavy and way too sensitive, replace the brake booster, I absolutely recommend doing that. The old servo contained about one liter of rain water, and as much rust flakes. It was surely not looked after, and never replaced (was a 1998 pert like the car itself).
p.s. don't think the TWG brake servo upgrade is really worth the extra x10 markup on the price. You just need to make sure the drain holes are not plugged, and avoid parking on an incline nose-down during a rain, and you'll be fine with the stock Lucas part.