hi Jax, i have used the 577 as its the high pressure version, works well, but i will only use it with a tapered thread, that is clean, i like the fact it locks the joint and no one can undo it without the knowledge that is... add heat and it will soften.
so you cant use it any where near a heat source.
i think its a good product
i hope this helps.
regards 

the 567 from memory is for low pressure only not 90kpa, that's what 577 is for, check the tube for its rating, as far as cleaning the thread I just wipe it dry.
I have had no issues as long as you are using it on tapered threads.
if you have had it fail I would expect its because the tread is no clean or defective. you must clean the thread if you are cutting it your self. when I do I clean the thread with good old fashion white sprits, or britolite. acetone works well too. 
I use gameco brand red sealant and its much better than the Loctite

regards