Manual Transmission Gear Box Oil - Wrong Grade?

So I changed the oil in the Transfer Box and Transmission Box last week at 51,300 miles. 2019 SZ5 Manual Transmission.
Up to now it has always been serviced at the Suzuki main dealer where I bought it from. According to the service schedule below, the two boxes don't need a oil change at any given interval if the correctly specified oil is used (Heavy/Extreme use is different).

 

Ever since day one when I got my Jimny, I have found first gear to be difficult most of the time (lucky if it went straight in first try), I have always resorted to trying 2nd first then selecting 1st gear, or it has just felt quite notchy. I have always put it down to a characteristic of this gearbox, and other people had found the same thing.

However, since changing the oil, selecting 1st gear feels like butter now, goes straight in, the notchyness has gone away!

I believe my Suzuki dealer will never have changed the oil, as it's not in the service schedule. So does that mean it might have come from the factory with the wrong grade oil in it?

Transfer Box drain plug.
 

  

Transmission Box drain plug.
 

 

 

 

Not sure about the 4 as mine hasn't enough miles yet but on the manual 3 main box it's really particular about being a gl4 not a gl5 or mixture spec. It's why I would only get transmission use oil from suzuki going forward, engine is different but all the rest are dealer supplies.

It could be a combination of new oil vs worn out old oil, synthetic vs mineral and a bit of placebo effect. There could be slightly more drag with the new oil that helps line the gears up.

Fully synthetic definitely affects the gearchanging, I changed the gearbox oil on my old Guzzi for fully synthetic and it seemed to make it noisier and it didn't feel "right" at the pedal, so I swapped it back to mineral. It could all have been in my head, but I swear there was a difference!