Yes, worn O-rings can lead to a leaky injector, as can the injector itself being broken. Pull the suspect injector out, and carefully inspect it for cracks. Check the pinholes on the engine side of the injector, make sure they're intact and clean. If all is good, replace the O-ring and re-install.
Also, fuel injectors being clogged is more or less a myth...why do you think yours are clogged? The pressure coming through there inherently prevents dirt from clogging the injector. More likely that there is a lot of carbon buildup on the inside of the intake runners and cylinder head intake ports...there are cleaners out there that can clean that up but I think they're only available to shops and certified mechanics (this is what shops generally do when they sell you a "fuel injection cleaning"). The injector(s) could also be broken and not atomizing the fuel properly.
1998 VW GTI 2.0