some are, some aren't. there are some horror stories but it depends on how their life has been. Mine has 198k on the clock now, no internal rebuilds yet.
thats impressive, what bhp is yours?
140-150bhp maybe, not been on the rollers.
the mods are:
De-Restricted air box (there is a restricter in the air box limiting the air that can enter the charger, easy mod just sanded it out)
Jabba R1 charger porting (removes material that restricts the charger outlet to produce more boost, a bit of charger inlet porting too)
65 - 63mm Toothed pulleys (the twin V- belts slip at high revs so this just spins it faster throughout the rev range, standard is 75mm but its hard to calculate the toothed equivalent, mine are custom and somewhere between 65 and 63mm)
GT inlet manifold (manifold from the G40's little brother the polo GT; has larger inlet ports and gives a tad extra top end power (tiny amount of low end torque is lost though but unnoticeable because of the torquey supercharged engine)
51mm Throttle body (standard is 45mm, i make these myself - check the traders section - ported at the top, frees up the top end revs and makes the throttle more responsive, great off boost)
Sorry for the long post, if you don't know a huge deal about G40s it can be confusing when people just make a list of mods that generally have community names; thought it would be good to explain it.