I have been putting off bashing the pivot pins out of the Ermes-Sub Double Roller mech that I purchased about 9 months ago and only just retrieved it from the spare parts box which I had tossed it into after giving it a quick once over when it first arrived. Now if you remove the rear countersunk socket head screw that forms the pivot pin for the line release lever and which has a biasing torsion spring wrapped around it and a nyloc nut on the inside then you will find that the sear lever swings right out because the only thing stopping that happening was the nyloc nut fouling on the rear step formed in the back of the sear lever. With the sear lever swung through 180 degrees you can pretty well see everything, so really no need to hammer the pivot pins out. The roller sear tooth has a rolled steel split drive pin forced through it and that pin has about 2 mm fore-aft free play in the small vertical side slots in the housing walls. That drive pin is only there to stop the roller falling out and keeping it in the correct lateral orientation in the sear box. The answer to the mystery as to why a square cut spear tail notch will roll this mech is the curved sub-circle cut-out in the sear arm as any fore-aft force acting through there has a downward component as the curved face is in a sense angled. My guess much earlier based on a modified non-roller diagram is pretty much what the mechanism looks like inside except that the backing projection is located a bit further forward than I had thought it was. The backing projection serves to block the line release arm from moving until the sear lever falls and rotates it out of the way. The sear lever has no biasing spring, so if you hold the mech upside down then it will not "dry fire" as it needs gravity to drop if there is no band load on the spear.
Note the two nylon washers that flank the sear lever and are mounted on the peened over sear lever pivot pin. The ends of the pivot pins are peened over to prevent you pulling the mechanism apart, although a determined whack with a big center punch and hammer would soon knock them out if you really needed them removed. The split drive pins can be easily removed with a small punch such as the one passing through the roller tooth. The front roller on the nose of the sear lever has a fat axle and not much roller, which is good.