Cannondale with 1.5" steerer, forks need attention

Hi, bit of advice really.
I’ve got a Cannondale Trail SL2 2010 model with RST Deuce Air 100mm forks, bike has been brilliant but now ready to sell, the forks themselves are great, really responsive to small bumps as well as bigger ones.
Only issue is there is a “loose headset” type bang at the front when going over rough ground. Had it checked out, not the headset, or wheel, it’s the fork! I pride myself in honesty and wouldn’t sell someone a dud.
Cant decide whether it should have a fork service, or sell with issue highlighted, or buy another fork. Ideally I don’t want to be spending alot of money on a bike I’m selling anyway.
What do you think?

I wouldn’t waste money on servicing a ‘cheaper’ fork, just sell it factoring it into your sale price (money saved on the servicing). Advertise it honestly..

Sell as is.Let the buyer know and make their own mind up about it.

on completely different tack – I have a minty pair of X fusion velvet 100-140 1.5 straights, was planning to sell next month

Thanks I appreciate all the feedback, it’s what I think is best too…. admit the forks need attention however everything else is sweet! I know bikes that squeal and squeak and this is a great bike so someone will get a great runner!

Thanks too Towzer, that is the other option but I’m going to see how successful I am selling the bike as is. Next bike is a lot more money so I need as much as I can!!