What tonearm will better mine?


I have been running a 12" Jelco SA750L with an upgraded Decca Super Gold on a Garrard 401 for a few years. I'm happy with the sound and happy with my pre, power and speakers. (Croft 25R, EICO HF35s, -good tubes, Quad 57).
I keep hearing that my tonearm is a weak link even though it sounds pretty awesome to me. What would it take to replace the Jelco and make a significant improvement? What should I expect to hear better? Would I have to drill the massive plinth? Thanks.
noromance
@2channel8 Thanks for the link. Interesting. I added the oil at the start and when it evaporated away, I didn't really notice any loss so I haven't bothered refilling it!
Why dontcha try something different and modern...
Terminator T3Pro fits nicely DECCA cartridges, the designer Vic at Trans-fi Audio used the London Reference as his main cartridge, see his site. And yes, you can adjust VTA on-the-fly with digital scale.

Btw, I use low impedance values for my MM carts. 30 kOhms sounds better than 47 kOhms w/ my Audio-Technica and SHURE carts, they also benefit from very low capacitance values like 100 pF of total value.
Yup Harold, the Terminator is a fascinating arm. I have one on order, should be ready maybe later this month. Mine is being made with an uninterrupted run of silver wire from cartridge tags to RCA plugs, a pair of KLE Absolute Silver I just shipped to Vic. Pics on the TransFi site show a London Reference mounted on the arm, which is what I will be using on mine.
I have a 12" Jelco SA-750L, and a London Decca Super Gold, with the DeccaPod, and a Yamamoto "African Black Wood" headshell.

It is the most obviously RIGHT combination that I have ever experienced.
If you do decide on a VPI 3D arm...also seriously consider the 2nd pivot modification.