before you start removing the gearbox, inspect all the coolant hoses in the area.
Besides the hoses to the heater valve, there is a hose that runs from the end of the water pump plenum to the bottom of the intake manifold. a leaky hose or loose connection there will cause coolant to spray onto the gearbox/transmission bellhousing.
There might be a welsh plug (freeze plug?) on the rear face of the block inside the bellhousing area (been a while since I physically looked there
). If that plug were leaking, most of the coolant would escape onto the backside of the flywheel and leak out of the bottom of the bellhousing at the clutch inspection plate.
Take a look at part two of the the downloadable '88 Samurai Factory Service Manual at Ack's FAQ (search for factory service manual
- the link to Ack's FAQ is in my signature, below) for pictures of these hoses.
BTW, the 1.3 engine has changed little since it's introduction in the SJ-series way back in 1986. Only the engine electrics and intake setup are different in various vehicle models.
I hope that this helps!