L.L.
I absolutely think resolve works best...the spot remover, not the "high traffic" carpet clean. Use the kind that comes in a spray bottle, not the can.
Spray on a liberal amount, let it set for 10 minutes, then take a damp rag (wet, then wring it out) and scrub, scrub, scrub. I have gotten out countless old and set in stains this way. If it only comes out partially, let it dry, and repeat the whole process.
That does a better job that the carpet cleaners I have hired to clean my carpets.