1951 Seeburg M100B issue help please

Hi
I am a brand new member to the forum. I have a number of vintage record players etc and just added another juke box to my collection.
Anyway, I saw this Seeburg advertised. I went for a look and the seller showed me this Selectomatic that was his late fathers. In the family home for 50 years.
The seller is the son and has no interest in it at all.
He plugs it in, turns it on and away it goes. It switches records and appears to be working well.
Then it stopped. He was stumped and said it has always worked perfectly. After looking it over and running the scan switch, and on off switch, it worked again. So I bought it and brought it home. I plugged it in and same thing. I fiddled and checked. By removing the plastic mechanism cover and flipping the reset lever up manually it will grab a record and play it when I operate and release the scan switch. The record will play fully, but then the reset lever will flick down and it stops before returning the record to the magazine. I have looked closely at the contacts and printed the manual out and checked the clearances, which all seem pretty close to spec. What might be causing his?
This machine also has a tiny button on the upper rear to switch to the next record. I don't see this in the manual and assume it has been added. It worked well at the sellers house, and when pressed the mechanism will click to switch to the next record, but it then stops before returning the current one.
I am still getting familiar with the Seeburg machine but I have the ability to fix almost anything. I just need to learn what to look for with this unit. Thanks so much.

Hi Demon,
Welcome !
One quick question--are both of the "service switches"pointing" in the same direction ?
If you had read the manual, you would know that this model does not return the record fully to the rack after playing the last selected record--that's normal-- If it is quitting prior to, selecting "pulled pins", it indicates that the Solenoid Assembly Unit is in need of a "rebuild". Ron Rich

Thanks Ron,
the funny thing is it was working the day I looked at it, and then after a few songs it quit. The seller demonstrated to me the little pushbutton on the rear to switch to the next record which was working fine. Push the tiny button and it would change to the next record with each press. He told me it was set to play all the A sides one after another all the way across, then switch and play all the B sides all the way across and so forth. He definitely did not know much about the jukebox and I have never had a Seeburg before. I only just bought it and so far have not gotten it to play more than one record at a time and that only happens by lifting the reset lever and lifting the scan switch to get the motor running. Once it loads the record it plays it completely, then clicks off, leaving the record in the turntable as you mentioned.
The selection buttons seem inoperable, and the coin mechanism has been set to bypass the coins to the return slot. Maybe I need to set the coin mechanism back to accepting coins and see if the push buttons will select the desired records. I have not tried that yet.