I honestly would have purchased from Guven when i needed to for my jetta glx, but I opted for the EARLY BFI kit, (which later proved to be a mistake) faulty drain...
when I did my Passat, (on a budget) I just did the plastic kit from Gap. I figured, the original lasted 120k, the replacement will last a similar amount of time.
but to the OP,.. there's several options out there. just make sure you flush the coolant properly and thoroughly before refilling it. you should replace the thermostat, and the housing and all seals/gaskets related....this is a good time to replace any questionable hoses or the expansion tank which is probably brown and stained.
if you purchase from gruven, check out their upper coolant hose Y valve, it's a nice replacement for an otherwise annoying plastic part on your car that will probably fail also.