If there voltage regulators are still overheating, then it must be dissipating too much power compared to what its package / heatsink size is rated for.
And the excess power must be either too much current being drawn from them OR there's too much voltage being dropped across the regulators.
So it's probably a good idea to measure the Input voltage & the output voltage, and check that these are correct with what's on the schematic / in service manual.
If the output voltage is much-lower than it should be, then this could be either because > 1.5A is being drawn from the regulator or there is an issue with the feedback resistors. Having a much-lower output voltage, with same input voltage ./ current, will also cause more power dissipation in the regulator.
And should be able to measure the current being drawn, by either removing a series-component like a low-value resistor or the regulator's input / output pin, and inserting an ammeter (DMM set on Amps).
I couldn't easily find a service manual / schematic on the 'net for this, to look at. But someone did manage to get the schematic from TTI, without having to buy the service manual, in this ppast thread:
https://www.vintage-radio.net/forum/...d.php?t=128051
Where it seems the (obsolete?) output stage transistors are a common failure, as they are also discussed, here:
https://www.eevblog.com/forum/repair...-function-gen/
If there is a a short / overload in the output-stage, then this might be overloading the regulators etc.