I got a mk 3 and gave it a total stripdown, it was in turps for two weeks to clean everything. that done i found the sear spring in two bits, got another from local gunshop and yes done some swearing trying to get it in, secret is hold the trigger and sear together, push the two bits up into the housing, once located use a fine tapered punch to hold the two componants together, once you have got them in, follow up with the pin, if your pin is to worn, use the smooth end of the right size drill bit cut to size, i cut mine with a dremel and a fine cutting disk. worked a treat.