The owner of a garage used for a Banksy artwork should "cut it down", another beneficiary of the artist has said.
Dennis Stinchcombe said he received death threats after mural Mobile Lovers appeared on the doorway of his Bristol youth club in 2014.
He sold the work and used the proceeds to save the struggling club.
Port Talbot steelworker Ian Lewis said he had been in "freefall" since Season's Greetings appeared on his garage in December.
A plastic sheet has been placed in front of the garage in the Taibach area of the town to protect it, but Mr Lewis said he had been left "stressed" by people trying to chip bits off his garage.
Mr Stinchcombe said Mr Lewis should act quickly: "If he's got any sense he will cut it down and put it somewhere very safe, until he works out what to do with it.
"The longer he leaves it the worse it is because anyone who's anyone wants to put their tags on it."
He credits Mobile Lovers with saving the Broad Plain Boys' Club: "We were 120 years old and needed about £120,000 to keep the club going...
"I had one or two offers of £1m. I also had a couple of death threats because I'd taken it down off the wall... [people claimed] I'd stolen it.
"In the end the police came down and took it to the police station and locked it in a police cell overnight.
"The Bristol museum then agreed to accept it and exhibit it until ownership was sorted out."
After the row over ownership, Banksy, who attended Mr Stinchcombe's boys' club in the mid-1980s as a teenager, wrote to him to authenticate the work and say it was the club's property and he could do what he wanted with it.
Eventually, Mobile Lovers was sold to a private collector in the UK for £563,000, with £403,000 going to the club.
Seven projects around Bristol then received £12,000 of funding, while the Broad Plain club was able to undergo a huge refurbishment.
"The work this has done to the young people of Bristol is second to none," Mr Stinchcombe said.
"Without that happening we would've shut. Banksy did Bristol a massive service, for which I will always thank him until the day I die."
What happened to other Banksy artworks?
Spy Booth, Cheltenham
The Spy Booth in Cheltenham, which took aim at GCHQ in 2014, had a complicated and relatively short-lived time as a mural.
Painted on the wall of a listed building, it was covered almost immediately in scaffolding as the owner of the house received offers of about £650,000 for the house.
But the work was not sold or moved, before being vandalised several times and gained listed status along with the house in 2015.
The house was sold in January 2016 and Cheltenham council told the new owner remedial work needed to be carried out on the property.
However, during the work, the Banksy was removed and crumbled into pieces. The council looked after pieces and returned them to the owner in 2017.
Art Buff, Folkestone
The Bristolian artist was busy in 2014.
His work Art Buff in Folkestone, Kent, showed a woman staring at an empty plinth.
It was vandalised after someone drew a penis on the plinth, before the owners of the property shipped it to the US in an attempt to sell it.
However, a High Court judge ruled the work should be returned to Folkestone, so the owners of the house could not sell. It is currently in storage.
The same pair later found one of Banksy's largest works - a man chipping away at a star on the EU flag - on another one of their properties in Dover.
Gorilla in a pink mask, Bristol
One of Banksy's earlier works, a gorilla in a pink mask on the wall of a former social club in Eastville, Bristol, was mistakenly painted over.
Saeed Ahmed, who bought the property in 2011 and whitewashed the wall, apologised, saying he "thought it was worthless".
He added: "I didn't know it was valuable and that's why I painted over it. I really am sorry if people are upset."
The building was turned into a Muslim cultural centre.
Anti-immigration birds, Clacton-on-Sea
Another work from 2014, Banksy's work in Clacton-on-Sea, Essex, showed several pigeons holding up banners demanding an exotic-looking bird goes home.
The town was readying itself for a by-election, which was won by Douglas Carswell, of UKIP.
But the work was painted over by Tendring council - a move labelled "moronic".
Girl With Red Balloon/Love is in the Bin, Sotheby's auction house, London
One of Banksy's spray-painted canvases, Girl With Balloon, was auctioned at Sotheby's in London in October 2018.
The painting was sold for £1,042,000, but the canvas promptly shredded itself upon sale.
Banksy later posted a video explaining he had hidden a shredder inside the frame of the painting, but admitted the shredding had not completely gone to plan.
The woman who bought the painting said she would keep it.