Gear Selector Detent Plug Removal

My 88 WR250 is a little tricky to change through the gears, I reassembled the engine in a hurry a while ago and wonder if the ball was in place which detents the selector drum. I thought I'd drop the plug from underneath and double check but its a plain steel plug with no visible signs of how to remove. Can it be removed or do I have to split the cases to satisfy my curiosity?

That plain steel plug as you call it doesn't seem to get a part number Kind of like the steel inserts for the crank bearings I guess. I never thought about taking it out. What I would suggest is removing the clutch cover, inspecting the spring that kind of straddles a peg, grag the shifting drum with something you can turn it with (perhaps just a 10mm socket it that doesn't unscrew) and evaluate whether it is in the cover or inside the cases. I would expect most folks do something along those lines pretty soon after putting the case halves full of all the parts back together. Not sure quite how it happens but the rod that has two shifting forks on it was somewhat bent and upon going to a parts engine the same thing was the case.

Wondered if I could drill it, tap it and slide hammer it out or simply unscrew it. It either pressed in or screwed in there but which one?

you would probably have to heat up the cases first, i have a knackered case here that i could experiment with but i leave for the uk in 4 hrs for a month, the spring bearing is a pretty hard/tight fit i cannot see how it would be put in wrong unless you left it out completely, mine was an absolute pita to install as the pring seemed too strong to push down all the way.

Problem is I didn't re-install the selector drum. The engine had been split to replace the crank seals by A N Other and the drum was still in situ. Me making assumptions has left me in doubt. I will be removing the clutch cover this week to replace the water pump seal, I'll make the checks Frank suggested above then. I don't want to split the cases unless I have to as they are as tight as a tight thing.

Any other tips?

I removed the clutch cover today, all was well. I drilled and tapped the detent plug with an M8 thread and used a slide hammer to pull it out, The spring and ball were fine and in place. Plugged the m8 hole with threaded bar and Loctite, Hammered home the plug and the gear box now works a treat ! Bit difficult to find neutral but all the gear select beautifully.

I have a similar problem with my 1985 400, I have accidentally put an incorrect size detent ball ( 8mm instead of 9mm) in my motor, and now it won't shift or even come out again. I tried using a press to get the selector drum out, but it won't budge. I am now afraid that I will have to go through the same procedure as RTM here above. All I'm asking for is a little more detailed info on how the fix was carried out.
My idea is to drill a 9mm hole through the plug to extract the spring and ball, and then seal the hole off by tapping and putting an m8 bolt in the hole.
Any answer is appreciated.