Not DEC related but still hoping for some help: Problems w/ LJ 4+ Printer

[Ali]

I rescued a LaserJet 4+ printer that I have been trying to restore.
Initially everything seemed ok and it seemed as if there may be just a bit
of an issue with paper pickup which I attributed to old paper in the tray. 

However, soon I started getting the accordion paper jam which led me to
replacing all the rollers including the transfer roller. Now the paper flows
freely! However, I am having a new problem with printing. When I print, the
first 5-10 pages initially come out blank. The printer does not produce any
errors or error codes. The blank pages are warm (not hot though) as expected
out of a LJ.

After closer inspection it seems that the pages are printed SUPER light and
gradually get darker the more I use the printer continuously. Eventually the
printer starts printing continuous crisp black pages like new. This is a
whole page phenomenon (i.e. not gaps, missing areas, etc.). 

A picture of the effect can be seen on VFC at:
www.vcfed.org/forum/attachment.php?attachmentid=52120&d=1554074105

Sorry for the poor quality picture.

Things I have checked/tried:

1. Using a brand new NOS toner (according to HP toner does not go bad as
long as it was sealed - which this was)  
2. Swapping the new transfer roller for the old one - same problem, I have
to print out a bunch of pages until the printer starts acting normally.
3. I have checked the HV and an image is being transferred to the drum on
the toner cartridge.
4. A visual inspection of the fuser shows it to be ok. 

Obviously this is happening printing demo pages so it has nothing to do with
computer, OS, SW, drivers, etc. Anybody run into this before? Any
ideas/suggestions. My Google fu turned up a bunch of discussions on the
laser door not being aligned correctly but that would seem to be a more
permanent issue i.e. unless you fixed the door no pages should print ever.
Mine gets better on its own after a number of pages are printed. Plus the
door and spring are fine - I checked them just in case. 

I tried posting on FixYourOwnPrinter.com but for whatever reason the site
was not accepting the question. Any other forums you guys would recommend?
TIA!

-Ali