Hififile, I have a suggestion that you might try.
After applying the Last solution, REWASH and RE RINSE the LP as if it had never been washed. This is best with a VPI machine in my experience.
The positive aspect of LAST remains, but the rewash pretty much returns the LP to the original sound (before applying LAST).
Gruvglide changes the sound as well, but rewashing after application removes the Gruvglide and the benefit it provides.
To my ears, Gruvglide somewhat compresses dynamics while rolling off the extreme high frequencies. It appears the cartridge brand affects the differences between these two products and the outcome of the test.
Those using Benz, Koetsu or Transfiguration (to name a few) usually prefer the Last treatment. Those with Clear Audio Insider or Van den Hul often prefer the Gruvglide treatment.
I'm guessing here, but this must be somehow related to stylus design, suspension and a combination of tracking and set up procedures for that arm / cartridge combination.