You can find cheap coolant expansion tanks on EBay.Part # 996 106 14708 . Whenever I contact the seller they concede they are not OEM. They are aftermarket of an unknown manufacturer and from an EBay Seller with less than perfect Feedback. Price is $90.They claim to offer a warranty but provide no details !
Note this seller claims in the Title of the Listing "PORSCHE..Coolant tank" -but it is
not Porsche - it is no-name generic of unknown quality with no written warranty.
The labor in the task of replacing the tank is such an issue that the risk/savings just are not worth it IMHO.
Porsche Radiator Overflow Coolant Tank New with Cap | eBay
Plus the seller "Arbosha"of SVB Imports Montrose Ca., has a murky rep on an MB Forum:
http://mbworld.org/forums/c-class-w203/301239-ebay-seller-alert-arbosha.html
http://www.yellowpages.com/sun-valley-ca/mip/svb-imports-456273818?lid=456273818#reviews
There are several fitting problems with the knock-offs:
1.the coolant level sensor(in the bottom of the tank) will not fit without removing excess material form the new tank.Do not force the sensor in -you will break it!
2.The drain nipple is blanked off. So if you overfill or it 'burps' ,it will overflow the shoulders on the top of the coolant reservoir and flood the electronics in the trunk.
3.The flange that fits on the bulkhead is oversize.Trim it or you will have breakage/leaks.
These junk parts make an already tedious job a ridiculous hassle.
Note:- the only review of a Pelican aftermarket coolant expansion tank(996-106-147-08-M127) had a failure. But at least Pelican would handle the issue honorably .It is $228.The OEM is $383.
2001 Porsche Boxster S Convertible - Radiators - Page 4