Count yourself fortunate to have the original 681eee stylus, depending on the hours and condition care of the stylus and records it may still have a lot of life left in it. I'v had a number of vintage cartridges and some of the stylus with low hours needed nothing more than a good cleaning to remove built up gunk. None of the aftermarket stylus will equal the original in sound quality, Expert Stylus in the UK may be able to retip your stylus if needed, cost about $160, should be good as new with original sound quality, I'd consider it a bargain.
Not so fast. Some of the
very old aftermarket versions come frighteningly close to the originals. You just have to find one - not an easy task. They rarely show up on ebay, and sell within minutes (assuming a decent BIN price), so you have to be quick, and know which brands are up to the task.
I run aftermarket styli on my 681EEE and 881S more often than not, and can't tell them apart from my NOS originals. They were all made in Japan, I believe, and are wonderful.
I do wish JICO could master the art making truly excellent replacements (like they seem to do for Shure carts), so we could have a current, reliable source that is an alternative to sending out for a re-tip. Also, member Needlestein knows the currently available replacements that are inexpensive, yet good quality - if you want to save some $$$. I have not tried those, but trust his judgement, and extensive knowledge.
This may sound discouraging to the OP, but don't lose hope. Finding one may seem like finding a needle in a haystack (no pun intended), but man, what a rush when you discover them.
So, what models do you want to keep an eye out for?? I'll share my secrets. We are all in this hobby together. For the 681EEE & Pickering XV-15 carts, look for a Walco W-510STDE and Rivertone 2404-DEL. For the 881S & Pickering XSV3000 carts, look for the Walco W-703STDE, or Astatic NMR series - models ST115-qd, PL129-qd, and PL127-ed. These are all at least 30 years old, so few remain, but man do they sound sweet. The "qd" ones are true quadrahedrals. Doesn't get any better than that.
And as majick47 says, use your current stylus until it quits. I'm assuming it's a D6800EEE stylus - the best elliptical out there. I haven't heard positive things about the MK III version (wasn't it made in Florida?) or it's generics, but I'd love to be wrong about that.
In any case, the 681EEE cart is a keeper. Many, many loyal fans of this cart - including myself.