Trouble reading discs

This is a used machine bought on ebay. Problem has been ongoing but got worse this week. It reads occasional disc first time. Often I must reload multiple times to read. Sometimes opens without reading. There is a whirring sound, but not steady. Sometimes it gets jerky with playback when I can get it to read. Once it starts to read it seems to work O.K. until next time I use it. Tried blowing compressed air to clean dust. Reset all settings to factory default (it worked for a day).

Any suggestions?