Replacing front derailleur on old MTB

[Morat]

I recently bought my son an old Cannondale F700 which I thought was quite an epic bike for a youngster.
However the left shifter doesn't feel right (very slow return) and it often won't hold the position for the biggest chain ring and just falls back to the middle one. I took the cable off to try and set up the gears from scratch then the front derailleur pivots are very sloppy.. so I was thinking the best option is to just replace the lot (inc cable)
So, bearing in mind this is a 3x9 era bike currently sporting Deore shifters, are there any spacing/cable pull gotchas I need to look out for if I'm just replacing the left shifter and front derailleur? Does anyone have any recommendations? The current setup is a band-on top pull (pulling down) and a separate shifter with Magura Julie brake levers.

[Adam]

Before you replace everything, when there's no cable fitted, try squirting some GT85 in through the cable hole of the front shifter and then operating the levers back & forth a few times, and then re-fit the cable.  I've found that's worked a few times to rejuvenate old shifters.  That could save you some money and avoid ending up with mis-matched shifters.

[Morat]

Adam - thank you!
a PC Meltdown, a summer holiday and a couple of hours twiddling later, it's working. Some GT85 style squirting and the lever is clickety-boo. I've also replaced the cable inner and outer and while it's not perfect (I think the derailleur IS quite wobbly) it shifts down OK and it just needs a bit more thumb on the upshifts. I'll give it another once over in a couple of weeks when I suspect the cable/outer will have bedded in a bit.
Fantastic!

[Adam]

Excellent!

I think what happens is that over the years the original grease solidifies, preventing the ratchet holding onto the section for the big ring.  The solvent in GT85 (or anything similar) probably then loosens it up.

[drossall]

As noted here, I used GT85 followed by Carlube on advice. It's worked really well and, some months on, the shifters are still performing like new.

[Morat]

I went with WD-40 dry PTFE to hopefully give a little long term lubrication, but I noticed the little bung/screw was missing so I suspect mud and yuck will get in there quite easily.
I tried a wipe of bog standard silicon grease on the cable where the new outer sits, we'll see how that goes.

[drossall]

I'd used WD-40 before and not had it last as well, but YMMV.