Help with my espresso.

Hi,
I have a problem with my espresso. It used to be fine - not perfect
I'm sure but I liked it.
Now it has gone wrong, I can only explain the taste as tarry and
sickly, even sweet.
I have changed nothing in my setup.
Any idea what coudl have caused this? I am guessing something is up
with my machine given I've changed nothing else? Quite possible - its
a cheapy Gaggia Cubika, over a couple of years old.
Any ideas would be great.
Thanks,
Damian

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