What is inspection hole with rubber plug for?

[barnett468]

There is a rubber plug around 3 inches forward of the gearbox fluid level check bolt . I can see gears thru this hole but do not know if I need to add fluid in there or if it is just an inspection hole.

 

Thanks in advance for any help.

 

[czakky]

It shows TDC of either the right side=D or left side=S. Useful for valve adjustment.

[barnett468]

thanks, i don't need to worry now, lol

[LowRyter]

D =  Dis Side

S =  'Snot disside