I’m curious about the 105 series 5-speed manual gearbox? There’s an intriguing hole in it, what could it be for?
What? Hope is not what I’m thinking, fam! 
Water drain for the bell housing.
Ahh it’s actually to drain oil from all the leaking rear main seals.
That’s what mine is for 
.
HZJ105. It’s just a water drain.
Step 1: cut a hole in the box.
Fife
Step 1: cut a hole in the box.
I thought that was step 2. FiFirst, you have to get a box.
Fife
Step 1: cut a hole in the box.
No no no. Cut a hole in a box. Put your junk in that box. Make her open that box. After careful review of the pertinent evidence, I am certain these are the steps.
The glory hole.
Congratulations, it’s a girl.
Weight reduction.
It’s a birth defect. This is what selective inbreeding does to transmissions, people!
Looks deliberate? That area will only have fluids in it if something is wrong.
Your money.
Drain hole for the clutch housing, to prevent getting oil on the disk if there is a leak.