I haven't personally seen a fiberglass BUD that is Ku capable, they exist-but I haven't seen one. Fiberglass itself doesn't reflect microwaves (Which is why they make radomes out of it), so as mentioned above they embed metal mesh in the reflector, if the perforations are larger that ~1/4" it won't get Ku. Since the listing mentions LNAs, its probably a commercial dish from the late '70s, which means that it probably wasn't designed with Ku in mind. The suggestion mentioned by delta_charlie has worked pretty well for me, but only at night and with something like a mag-light. There is some great advice on this at geo-orbit dot org, click on "prime focus systems", scroll to the top of the page then click "choosing a dish".
(As a side note, the gain on a 12' dish at K band would be phenomenal, but very difficult to aim-a tiny fraction of a degree off and you've lost the signal.)