I asked because the cracking of locking block for that year of production seems to me a bit unusual. Throughout the years, starting approximately from the late 1960's Walther introduced a number of improvements to the P1 like reinforced slide, frame (steel hex bolt), hammer, sights etc. They also changed the composition of steel and design for the locking block. I'd assume that your 78 production model should have all these goodies. Apparently, it slipped somehow through the cracks and the block was not to the higher standard. Mine is 2/77 so I'll see how it works for the next 6,000 shots. Now I have 1,800 and the locking block is immaculate. I've read somewhere about a case of cracked locking block and since then I inspect it very thoroughly with a magnifying glass after each shooting.