Originally Posted by Pleiades

That is the primary symptom of the seized and gummed up bobbins you've identified. The discs should "float" on the carrier with a fairly light touch. If they are sticky or stuck the disc will tend to get marooned in one position or other and move jerkily (if they move at all) as you have found.

OE discs are cheaper than decent aftermarket discs (EBC etc.) on the front, so buy OE. You can get cheap Chinese wave discs but they are more trouble than they're worth!

Interestingly at the rear, it's a different story - the OE disc is double the price of an EBC item!

Provided you can get the disc bolts out without damage then they'll be fine to re-use with a thin application of Loctite. If in doubt though - change them. Don't buy OE bolts though as they'll end up costing you as much as the discs! Go visit your local fastener shop.

Fitting new pads with new discs is always advisable even if you think they are fairly new/good; especially so if the discs haven't been running true.