If a snap in, remove the extractor and reshape it (bend flatter) and be very careful when re-installing. It's not uncommon for the extractor to be bent so it won't spring out enough to engage the case. I've had them get sticky so that when chambering a round the extra friction on both ends causes them to bend, then merely hide in the recess and not spring back.
Once you get the extractor properly formed then make sure to keep a drop of lube on each end and regularly clean the area out. I spray mine with Brake-Kleen and blow them out with compressed air on a regular basis.
You also need to make sure that when the extractor clip is installed, it is free to flex back into the recess and spring back. The "hook" needs to slope slightly in toward the bolt face so that the case head slides smoothly over the "ramp" and the clip then snaps into the extractor groove. If there is a burr on the inner edge, polish it off with some 1500-2000 grit wet/dry sandpaper (available at most Auto Parts stores).
As for new extractors, I prefer to just replace the whole bolt. PTG makes some great bolts with either cut-outs for Sako style extractors or the M-16 type extractor (which I prefer and have on one rifle). The great thing about PTG bolts is that you can get a One Piece bolt and the handle won't "un-solder" under a hard pull. Their manufacturing tolerances are tight enough where the bolt I bought headspaced just perfect (factory barrel and chamber).
Now, if the extractor is riveted, just get a dental pick and use it to carefully reshape the clip in the recess so it functions properly. Remington Bolts have a recess in all of them that many would consider "enlarged". If the nose of a Remington bolt has any part of it enlarged it won't fit the recess in the barrel tenon and the handle won't come close to closing.