I would dump it. I bought a 50 L f1.2 from Canon, and THE DAY I bought it, I dropped it 1 meter onto padded carpet, and it didn't work right, sounded weird when I shook it, and squeaked when it autofocused. I should have quietly returned it and pretended I never dropped it, but instead I had it repaired by Canon, which they did for free. It works now, but it still has a squeak, and sometimes it will not focus to the MFD. When I ask Canon to look at it again, they say "It is fine, It is fine, no repairs needed." The whole situation has me soured on L build quality, and this happened a month before the R came out, so I look at my L glass now and wish I never bought most of it. If you aren't 1000% sure, send it back. They charge too much and do too little on EF L. Honestly, they should have a buyback program for all the people with huge EF glass investments who were waiting on Canon's "sexy" solution for mirrorless mount that didn't involve adapters, like they claimed they were doing. I feel a bit betrayed.