I've just researched the heck out of MM, MI, MCHO, MCLO, SUT, MC pre-preamps.
Many think rebuilding is to save money, however you have many other important reasons to rebuild that Sumiko. If you do, find the best to do it, pay what you have to, continue to love it!
I found, the channel separation and tight channel balance of most cartridges, any type, only becomes greater/tighter in the darn expensive range.
Your Sumiko has both excellent separation 30db and tight balance 0.5db. That is excellent, so, I suggest you rebuild it, or, don't go down in specs if you move to a new cartridge.
As it happens, I just left my beloved Shure V15VxMR with new boron/SAS stylus from Jico, to my first MC using SUT into my equally beloved tube preamp MM phono. The MC I chose, AT33PTG/II has same 30 db separation and 0.5 balance specs as your Sumiko.
After a few weeks now, I am certain it makes a more solid center, and a wider image, it won, the Shure went upstairs for a new competition in my office.
Remember, there is no center signal/reproducer, it is a Phantom, created by EQUAL left and right.
You also have the advantage of tracking 1.8g, my new AT wants 2.0 g; I prefer Shure's 1.25 tracking, however ...
If yours has enough volume now, then you skip the cost and extra device/cables/hum possibility of MCLO,
