Here is a nice original TD TF gearbox dipstick.  If yours is missing or damaged, don't expect to buy one from Moss Motors.  They are not available.  The dipstick has been bead blasted and is ready to use.  The graphics on the lower end are very clear.  

If you need to know how much lube is left in the gearbox after it has gradually leaked out, a dipstick is a good idea.  If your gearbox does not leak, then you likely don't need a dipstick.

Be sure to look at my other gearbox listings.