For really dirty records, try keeping the enzyme on the record for a longer period of time, say 10 minutes per side. You may need to add a bit of fluid so it doesn't dry out. Gently agitate the fluid with the brush while you stand there. One of the reasons for the popularity of ultrasonic machines.
Then again, the problem with some records is not dirt - in Julie's case maybe its not the cleaner or the brush.
And there's always that question: when should I stop cleaning?
In retrospect all the friction caused by multiple cleanings may have induced static into the LP.
In addition those old LP's may be thicker throwing my VTA off, and that increases surface noise.
I will check out these theories tonight.
This alternative methods of record cleaning via modification topic interests me. So much so that while looking outside normal avenues I found pond misting pucks (fogger), ultrasonic welders and transducers.
I sort of came up with a KISS method of my own as a result.
I might take my direct drive Technics and remove the headshell from the tonearm. Then attach somehow one of my wet record brushes, and using the counterweight of the tonearm set a very light amount of pressure.
To top it all off, set the table on top of my subwoofer and play one of those deep organ CD's I have. Not an ultrasonic shaker, a low frequency shaker.
If I do this I will post it, just try not to laugh.
I have to turn my Record Doctor by hand, so Joe C's DIY will not work for me.