Service Manuals
The above link is a fantastic repository of service manuals for a myriad of laserdisc players. It is by no means exhaustive, but a great many players are represented on the site. Referencing your player's service manual is a great first step to understanding the inner workings of your player. The service manuals provide exploded diagrams to illustrate how parts and assemblies interact with each other which can be a great help in figuring out how to remove one part that at first glance seems to be hopelessly embedded in a maze of other parts. The service manuals also list the part numbers for replacement parts. I try to list compatible players on my eBay listings for replacement parts, but when in doubt if a part applies to your player, take a look in the service manual to confirm.