Mercedes uses ATF in many manual Trannys.
My Isuzu manual called for a monograde engine oil in the (combined) tranny and
transfer case. That caused shiftability problems in winter, which were resolved
by using a oil called Castrol VMX (which is available on the SA market)
A 5W30 engine oil is bad news in trannys, since the shear stability is not
given. A ATF without friction modifiers (syn) might be a better choice, but
depends on compatibility with seals and other factors.