impossible to resist such a plaintive cry.... I shall try to help.
The 300 uses a T4P or P-mount type cartridge, this was a system partially adopted by some companies to standardise the size/fitting and weight of the cartridge to make replacing/changing easier, at first used on linear tracking decks.
First check that the arm is free to move and has no resistance, it's possible the auto mechanism grease may have thickened over time, or it could be catching somewhere, but if it seems ok and the auto return operates ok then the following will apply.
It's most likely only the stylus that is worn/damaged and causing the issues you describe, as you get sound and there is only minimal (if any) adjustment for tracking force. The only way to proceed really is to buy a new stylus, still available I suspect, but may be almost as cheap to buy a new cartridge and stylus assembly (the stylus accounts for most of the cost). New AT's should start from about £30/$30. A quick search for T4P will bring up options/suppliers/
Thers a user manual in the library, http://www.vinylengine.com/library/tech ... b300.shtml
But it's in German! Sprechen sie Deutsch? Still the pictures may help!