Hi @sunrisein2020 ,
Not what you’re after but here’s a link to a [https://www.manualslib.com/manual/1451716/Sony-D-E300an.html#product-Discman%20D-E300AN|service manual] for the player.
It gives a breakdown of the mechanical sections but unfortunately there is only an electrical parts list and not a full mechanical parts list, only a parts list for the optical pick up section.
May be of some help if you have electrical problems with the player.