Thermal paint/paste for transistor

[Birstall]

I have a Hafler DH200 amplifier (bought in 1981).

I have replaced the toggle switch but in the process, one of the round metal transistors fell off one of the output PCB's. From the circuit diagram i believe it is a 2N5415.

Around the body of the transistor is a 'winged' heat sink which is attached with a dark red 'paint' or paste. I have been unable to discover what this 'paint' is although I assume it's some kind of thermal medium

I'd be obliged for some guidance as what i can use to reattach the heat sink.

This photo is not mine but highlights the part I'm talking about.

Thank you.

[Gyro]

I suspect that it is just paint - the sort they use for locking preset pots etc. to stop it coming loose. The thermal resistance of the little tab heatsink is so high that thermal compound wouldn't make any difference against the sprung metal to metal contact.

[Rog520]

Thermal epoxy is sometimes used, but the heatsink wouldn't have fallen off if it was epoxied. Probably just a very basic glue...or paint.