The actor -- who's played the flamboyant fan-favorite Serge since the 1984 original -- tells TMZ 'Axel F' has the secret sauce that made the first two films '80s blockbusters ... namely, the entire OG cast is back in a story that's vintage buddy cop.

BP uses the metaphor of his beloved bird flying into a wall to describe the 'BHC3' flop -- but, the bird survived, and he says the series is mending in much the same way.

FWIW ... Eddie also recently blasted the 3rd film, telling Seth Meyers it lacked "a great villain," which shouldn't be a problem this time -- 'cause Kevin Bacon's playing the big bad in the new flick ... a plot twist EM spoiled on "Late Night" ... Oops.

BP says embodying Serge once again was a snap ... adding he's asked all the time to do the character by fans via Cameo ... so he had no trouble slipping right back into the role.

As for getting back together with the old gang -- which beyond EM includes Judge Reinhold, John Ashton and Paul Reiser -- check out the clip. Sounds like the crew's still tight as ever.