As Motorola made these units for Ford, no Ford Manual covers them in any real detail. There is a small piece in the 1967 Shop Manual (the 1966 Shop Manual has nothing on the 8 Track Player, as it must have been published too early to include something), but only on removal and a little on cleaning.
Motorola and Sam's Photofacts (an independent third party), did publish complete manuals for repair of these units. If you need a copy, send me a PM with your email address.
As far as playing "any 8 Track Tapes", that is not quite correct. It will play any 8 Track Tape except Quadrasonic 6 Track Tapes. In the mid-seventies, Ford (and others), introduced the Quadrasonic 8 Track Players and Tapes. These are usually designated by "Q8", and in addition, all of the Ford Quadrasonic Tapes were in RED plastic cases instead of the "normal white.
As for the Tapes themselves, here is a brief history of the early tapes :
"1966 "Ford Family of Fine Music" , C6AZ-18816, Original 8 Track Tape. These are extremely hard to find now, especially in working condition. The 1966 and 1967 Ford Tapes were Lear Jet Pak tapes, and while stylish in appearance compared to the later 8 tracks, these had inferior foam rubber on the tape "pads", which deteriorated after a short time (makes one wonder about the Lear Jets themselves), and sometimes actually "gummed up" the tape.
Knowing this, about 10 years ago, I had all of my Lear Jet Pak tapes professionally gone through. This included disassembling the tape case (which unlike the later tapes takes special tools), cleaning the tape insides, replacing the foam pads on all, installing a new "track changing" splice on all, all were cleaned, lubricated and adjusted, and the roller replaced if necessary. These tapes have only been played twice ; once by the professional who "restored" them, and once by me after receiving them.
There were six known 1966 Ford 8 Track tapes produced. These were marked PC8S 183, 185, 186, 203, 205 and 206. The PC8S 186 is marked "Stereo Demonstrator Tape", the PC8S 205 is marked "Mustang Demonstration Tape", and PC8S 206 is marked "Thunderbird Demonstration Tape". These are short 4 minute tapes, intended for Salesmen's Showroom use only, and not intended to be given away as "Promotional Tapes". I have never come across either one in my 40 plus years of looking. Nor have I ever come across PC8S 183.
All of the 1966 promotional tapes, and the majority of 1967 tapes, came in a white plastic "tray type" box, with a clear plastic "sliding" cover. While the 1966 and 1967 boxes appear to be the same, the "PC8S" number of the appropriate tape was printed on each box. In late 1967, the box was replaced with the "well known" cardboard sleeve".
I have been involved with 8 Track Players and Tapes since they came out (as well as the 4 Tracks before them), so should be able to answer most of your questions, other than major repair.
Hope this helps,
Bob