Hi, team_negative1!
I've been trying to find you're use of the HSL recombination technique (since your mention over at msycamore's THX 1138 "preservations" thread) -- if you caught my reply there.
I had better success in first equalizing the Luminance of the separations before recombination in muddyknees2000's The Hobbit Rankin/Bass Animated Film (see Page 4 that thread). In that case, ... The DVD was too dark to accurately carry the VHS Hue & Saturation. A "color correction" of the B&W DVD Luminance was first made to match the VHS Luminance (very easy with B&W only) before recombination.
You're having the same problem in this instance. The faded film's Luminance is too light for recombination with the LPP's Hue & Saturation, to accurately carry those colors.
So, after HSL-splitting the faded film and the LPP, you'll see their Luminances are not near enough to one another. Since you're adding LPP's Hue and Saturation to the faded film's Luminance, you'll want to adjust the faded film's Luminance to approximate LPP's Luminance ..
faded film LPP
faded film-L & LPP-HS recombination LPP
faded film-L adjusted to match LPP-L
faded film-L(adj.) & LPP-HS recombination LPP
BTW, there is a little mis-registration between the two screenshots that resulted in mis-aligned coloring. You would want to conform them to better line up, for better results (no "color fringing").