the Garrard 301 plater is concaved.

My early grease bearing 301 has a slightly concave platter too. I believe it is common. I believe it was made this way intentionally. If it bothers you, there are after-market platters on the market that offer slight benefits that may or may not be audible depending on the rest of your deck and system. Check out Peak HiFi in the UK. I bought Shaun's replacement brass bearing even though my original bearing looked brand new. I am a big believer in having the stoutest most precise main bearing possible. https://www.peakhifi.co.uk/cgi-bin/ecom.cgi?Command=ShowProduct&db_pid=718
https://www.peakhifi.co.uk/cgi-bin/ecom.cgi?Command=ShowProduct&db_pid=96

The original platter was not turned on a lathe. It was cast and then spun balanced with drilling of the heavier spots. I wish the chassis was also cast-but it was stamped. There is lots of literature available on this. EW Mortimer's book on the history of Garrard is a good start. 

My head is gong to explode. Google Art Dudley and Thorens and Garrard and read his essays. Don't believe Art Dudley, google Ken Shindo and Audio Note and Garrard. The Thorens TD124 and Garrard 301 were designed and built with a level of precision and craftsmanship and engineering that remains unmatched to the present day. Both were built to be used in the broadcast industry where it was common to run the decks 24/7 for months at a time. You apparently have a 301 so did you not do any research or listening comparisons before buying? Both do have their minor challenges. The TD124 platter sits low in the chassis and can create challenges getting a modern arm low enough. The Garrards require a plinth that is massive and arguably "tuned" to cancel out motor noise.