Lewie,
Yep you’ve got old Shimano brakes.
They are a bit of s pain to bleed solo, much easier with some assistance on hand.
Here’s a reasonable vid of a solo bleed but as you can see he’s swinging the calliper about and doesn’t have the line taught and vertical which is a great way to get a poor bleed.
https://m.youtube.com/watch?v=dFuwoEYvt_w
Also lots of stories of Shimano on brakes becoming borked after bleeding, they are very sensitive to other mineral oils, so I wouldn’t use anything other than pucker Shimano on mine and (touch wood) no issues.
Have fun!