The most common and most likely answer to this crossword clue is the 8 letter word TRICKLED
I've seen this crossword clue in The Times
T
R
I
C
K
L
E
D
Buddy explains!

The straight part
We know that "Ran slowly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ran slowly = trickled.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TRICKLED mean?
TRICKLED verb- To pour a liquid in a very thin stream, or so that drops fall continuously.
- To flow in a very thin stream or drop continuously.
- To move or roll slowly.