NC - 2nd Gear Synchro

I have a 2006 MX-5 and recently had the manual transmission oil changed at 30,000 miles. After the oil change I noticed shifting was rough, especially shifting into 2nd gear. The oil that was used was GL-5, which is what the manual recommends.

I did some research on the internet and switched the oil to Redline MT-90 as recommended by some Miata owners. It helped some, but still not as smooth shifting as it originally was. I still don't understand why.