THROW IT AWAY is my advice !!!

I done exactly the same with my old xr2 turbo grs cooler, flushed it till it was like new then when mapping it to 2.5bar boost it blew a load of swarf into the inlet and into the head and fucked the whole engine costing me 3k+

That why I recently sold my pro alloy cooler and had a custom 1 made rather than cutting it risking swarf etc getting into the core, most expensive mistake I've made with my cars! Never again