Gunk in coolant

Hi I hope I’ve posted in the correct place. Mini One 2003 1.6. 120,000 miles.

Car overheated a few months ago and I had the radiator bled and a new thermostat housing fitted. Seemed to do the trick but it’s started overheating again. I’ve been keeping an eye on the coolant and topped it up directly into the radiator last time as the coolant box was at max. That seemed to do the trick for short journeys the temperature gague was sat at half which is spot on. However, today it overheated. Got it home and had a look at the engine and the coolant has dropped to almost mine but it’s clearly full off a light brown gunk. I could also see that there is some kind of leak. Pls see two pics attached. The leak might just be coolant that I spilled a few days ago when topping up but my gut says it’s some kind of leak.

So, what with quarantine, limited money, time on hands I might take a look at this myself. Any thoughts?

I’m hoping it’s not the head gasket as I believe that’s pretty much the end of the car but are there any other things it could be? I’d really like to keep the car running for local trips as long as possible as just been MOT’d just before lockdown and don’t have the money for a new car.

Any tips/tricks/advice?

And a basic question - I am so not a mechanic somplease excuse of silly but - is a flush the same as a bleed? I know I had a click mechanic look at the car last time and he bled the radiator. Is that the same as flushing the coolant? He bled the radiator and then fitted the new thermostat housing and that definitely solved the problem for a while but now seem to have a related problem and would like to see if anything I can do myself.

Thanks for any help and hope I’ve posted in the right place.