My friends had me over and this poor tree looked to have fluid coming out of a very old wound. They say it was like that long before they arrived, is there anything they can do for the tree? Hate to think its been like this for years :(
Your friend should contact an arborist and not just a tree removal service. The arborist can determine whether the tree must be removed. The removal will cost more than just the consultation. A real arborist will carry professional liability insurance in case they're wrong and the tree falls later.
It has yeast eating sugars because of some problem inside the tree. This produces a lot of pressure, because of the production of co2 gas, and this is being released through a weak spot. That's what you see outside, it's leaking through the weak spot.
In the crown you should see dead branches and a weak crown. Most likely it has been damaged (badly pruned? ) in the past.
The long and short of it is that if it can cause damage when falling over, remove the entire tree and replace it, hire an arborist. If it doesn't matter and you don't care... Sit back and hope it's going to stay alive for as long as possible. Then just literally don't do anything, there isn't a fix. Just remove dead wood.