Battery drain by radio circuit

[dslc]

The circuit which includes the radio and cassette player in our old '99 Yaris is drawing almost 200 milli-amps when the engine is switched off.
Naturally, if the engine isn't run for a day or two, the battery can go flat - not good.
(From what I've read, a car - when all the electrics are switched off - shouldn't draw more than 50 - 75 mA from a battery?)
When I take out the relevant fuse - a 15 A - the drain on the battery drops to about 20 - 40 mA, if I recall correctly.
The down-side of taking out the fuse is that I can't have any music when I drive. But, perhaps more importantly, this circuit also powers the headlight beam indicator - so it would be good to get it fixed.

Has any one experienced this sort of problem before? I just wanted to make this enquiry, before trying to delve any deeper myself. The car is fairly old.
Is it likely that the radio is the culprit?
I need to double-check what else is on the circuit.