Groom seems pretty keen on the outside (5)
I believe the answer is:
preen
'groom' is the definition.
(a bird grooms itself by preening feathers)
'pretty keen on the outside' is the wordplay.
I cannot quite see how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is present in the answer.
The remaining letters 'pen' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'seems' acts as a link.
Can you help me to learn more?
(Other definitions for preen that I've seen before include "Tidy and clean (plumage)" , "demonstrate pride" , "Groom with elaborate care" , "Titivate oneself" , "setdown straight?" .)