2004 KTM 125 sx transmission confuses me

I got asked to help with one young boys KTM, who lives in the same town than I. The engine was full of dirt, top end broken and was delivered to me in pieces. Everything is clean now and just putting it back together is left. But I got stuck on assembling transmission. Bikes engine manual (written by KTM) says that there should be one more sprocket. The sprocket never got into my garage and the owner of the bike claims that he brought all of the parts to me. He said that bike has 5 gears.
I'm now thinking that transmission axles are now like they should be and by adding that one missing sprocket where there is red ellipse in picture, and changing that one part from the other axle (red arrow), bike could be converted to 6 speed.
Can anyone confirm is this so?

 

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I know you can do it on some of the other bikes (I want to say 450 xc-f into a 6 speed) by doing pretty much what you said.  There's a writeup over on ktmtalk somewhere.

You are missing a two gears. Those dogs need something to engage to.

I've looked at my 2005 manual for the same reasons, 5th gear is to slow.From what I see you should be able to use both 6th gear ratio from an EXC 125.Everything else like shift drums use the same part # from one to the other. 6G20 idler gear (50333009100) and sliding gear 6th 6G20 for the countershaft (50333005100  should do it.I've never had mine apart yet so I'm not the expert but when it comes apart I'll do mine.I see the same as you, looks like idler gear should be there on the main shaft,? call a dealer  see what they say?

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