Willing to be proved wrong.

Your old Stanton cartridge, while good in its day, is probably due for replacement since it is very likely that the rubber components in the cantilever suspension are deteriorated due to age. It's possible that you can find someone that can rebuilt the 681EEE, but I doubt it makes much sense financially.

The tonearm on your Garrard turntable is not a very sophisticated model, so it does not make much sense to buy a top-end cartridge for it. Something like your Stanton should be fine, as would a Shure M95ED, or one of the less expensive Grados.

I think you'd be best advised to contact either Jerry Raskin's Needle Doctor, or Garage-a-Records (which is often cheaper than the Needle Doctor), to get their suggestions on a good moderately-priced cartridge that will work well with your TT/tonearm setup. Here are the Web links:
1. Needle Doctor: http://www.needledoctor.com/
2. Garage-a-Records: http://www.garage-a-records.com/

I agree with Sdcampell, and since you're not going to spend anything on a new TT now - and since your TT won't justify a pricey cart - if I were you, I would probably take this cost-savings as an opportunity to not totally cheap out on the phono preamp while you're having to get one, just in case you get hooked and want to go for a better TT/cart later on (and somehow, I doubt this will take very long - but if you don't get hooked, who's gonna want to buy a used RS unit?). If you get one of the inexpensive Grado Prestige carts, you might look into their own battery-powered phonostage (presumably optimized for Grado MI carts, but should also work well with Shure's high-output MM's), which is not terrribly expensive, and should still do a good job for you if you move up to one of their wood-bodied models in the future. But if you decide not to go the battery route, Mikey Fremer seemed to like the Gram Amp the best of the inexpensive phonostages he's rated recently.

You'd be surprised how good a Stanton 520 SK cartridge will sound. For less than $40, it comes with an extra stylus. You can find them at a Guitar World store, or check around online. They're readily available and well worth the price for performance.