I've just ordered my third Heater Valve in two years.   The original
one worked for about 6 months, then failed in a way that it would
never fully block the flow of hot water.  Eventually, the little tab
that stops the motion of the lever broke off (probably 'cause I was
pushing it too hard in frustration when it began failing to close
fully).  Replacement #2 worked about 3 months, then developed a leak
from the seam -- it drips coolant when the system is under
pressure.   I'm hoping that #3 will be better.

Did I just get unlucky?  Or has anyone else noticed a batch of bad
heater valves? (part # 171 819 809E)

I notice prices on this part are all over the map -- Under $10 at
some vendors, up to $20 at others and the dealer.   Is there an OEM/
aftermarket difference?  If so, what is the "good" brand?