Leaking Oil from Transmission? Loose nut

[spikebites]

Hi,

So I've been having this problem I guess for awhile, but I never noticed it until now.  This has been happening for 2 years.  Next to my fill nut on my transmission, a black powder keeps forming.  I have included photos.  If you wipe it off with a paper towel, it just flakes off.  I'm assuming this is the transmission oil.

I didn't think much of it, until there was a heavy smell of transmission oil after a ride one day.  I went to loosen the nut, and I noticed that it is no longer tightened.  The nut remains in but it has maybe a cm of give.  If i twist it left, it will not unscrew unless I twist left while pulling.  Then I am able to remove the nut.  When I turn right to tighten, the nut just keeps spinning. 

How difficult is this repair?  And what would you recommend I do?  I feel like I've lost a lot of transmission oil the past 2-3 years riding along not even noticing this has happened.  How much would a repair like this cost at a shop?  Should I drain my transmission oil, and refill it in order to drive to a shop?

Thank you,

[Ruffus]

@spikebites welcome here!
Your assumption this being gear oil COULD be right (judging pics). COULD (since the whole gearbox is oilcovered) also be too much oil in there and it blew out through this breather hose.
Check this before further steps.

If there is NO oil oozing out when you remove the drain plug, there is already emergency happening in your gear box.

The transmission oil check and drain bolt on the Kymco Downtown 300i uses a 12 mm socket size with an 8 mm (standart) thread diameter.
Key Specifications:
• Socket / Wrench size: 12 mm
• Thread size (diameter): 8 mm
• Tightening torque: 1.8 – 2.2 kgf-m (19.7 N-m)
• Recommended oil: SAE 90 gear oil
• Transmission oil capacity: 0.23 liters (at disassembly) or 0.21 liters (at change)

So, seen this specs there are three possibilities, depending on your skills:

A) pull the fill plug out and set an stainless steel thread, called HELICOIL or similars.
Inexpensive, professional and secure (see pic).

B) fill up oil and drive to a dealer who does the same.
Depending on where you located at it will cost between €20,- and €100,- without further complications.

C) take a tap and tie set, cut a 10mm thread, put a short 10mm bolt with a gasket in it.
Costs € 2,- and having a tap and tie set.
Driving w/o gear oil costs you a whole engine!
Come back for Qs.