When you bolt everything back up the ‘factory’ procedure is to clean and coat the bolts with 3M EC776, this is described as a lubricant sealant and is a sticky, volatile goop requiring its own even more volatile cleaner. My understanding is that it hardens off in air, so once the water pump bolts are withdrawn they should be kept ‘wet’ by storing them in paraffin.
As a modification, complete sets of replacement bolts in stainless steel are easily available (eBay) and may help on any subsequent replacement.
