Problem with shifter not going into gear

Gday . This is my first post on here. I drive a metallic black 1998 model Jimny. Not long ago I had to replace the gearbox due to the old one having worn out bearings and a selector shaft had a massive chip out of it. In the process of replacing it I saw my that my Manuel shifter had a little plastic bush that had completely fallen apart into multiple pieces. So I ordered directly from the Suzuki store a replacement Bush which was slightly shorter than the original. (Because it came from the Suzuki store I figured surely it wouldn't matter since its an orginal part). Anyway I have finished putting it all back together and the car runs so much nicer without the loud blurring noise in high gears. Thought now I have a problem with the shifter not going into the gears occationally. So I pull up at the traffic lights and I can't get it into second. I've tried double clutching it and forcing it in but it won't go so I'm left having to rev the guts out of it taking off in 2nd. This occurs in all majority of the gears. I'll be driving along the highway in 4th and I can't get it into 5th I then have to wait for 30 metres down the road try again and it will go.
So my question is how do I fix this ? Is it a problem with the gearbox I put In or is it to do with the Manuel shifter. Any help will be appreciated. Thank you

try to take out the plastic bush and place it again in place and do not tighten the screws too much i had same issue and changed the plastic bush now ok