I purchased a set of front and rear grooved/drilled discs for my MY99 late last year and fitted them just before christmas. With Mintex pads they came to £200 from the seller Mtec100 (who has very good feedback). After only a few miles they started juddering which steadily became worse. I took the car to my local auto engineer and they examined them (suspecting contamination rather than warping as they were so new), however they found a large black mark and streaks on the insides of both fronts. After puuting them on a tyre balancing machine they discovered they were warped. Upon close inspection they saw that the entire inner area, but particularly the darker area (which had now been sanded clean) was fill of millions of 'holes', where the discs had corroded..in less than 1000 miles!! This gave the resulting 'grabbing' feeling on the pads. The car hasnt been driven hard and has only averaged 150 miles p/wk, yet the discs look years old. The outer edges and centre drums are also very heavily corroded with rust. To add insult to injury there is also evidence of cracking!! I now have to return the discs before i can get my refund. My advice...if yore tempted to buy MTEC100 brake discs then DONT. They are rubbish. unfortunately im prevented from posting threads on this forum (?) but im happy to if someone knows how i can make this option available.
MTEC100 Subaru Impreza Brake discs..youve been warned.

 

usual ebay rules apply. you gets what you pays for.

you can get the odd bargin though!

 

that's porosity in the casting mate, normally the sign of a poor casting process.

drilled holes on a porous disc, not a good combination no wonder it warped, more than likely a chinese cheapy casting. no way you could have known this, best of luck getting a result

 

Yes drilling a disc is not a good thing with good pads , as they will crack , if you get a refund , I can supply you a pair of grooved discs , with a 12 month guarantee against warping even if you do track days , currently on offer for £69 a pair , and these are good quality blanks.
Some see the bargains on ebay , and most of the brake stuff on there is chinese crap !
Good luck with it
Cheers Ian