Bit the bullet and decided to change my water pump. All but two of the bolts came out. The long ones were easy as the timing cover was off last year. The two broken ones one came out with a stud extractor the other snapped closer to the cover. I managed to drill it down the centre. With a bit of heat and a pair of grips I managed to remove the last bit of stud. I decided to replace all the bolts which are 1/4 UNC. I got inch and a quarter long from Kayfast. Had to wait a couple of days for the bolt to arrive. Once here carried on. Now with the pump bolted to the cover I went to fit the pulley and fan. This is where my next problem showed itself. The original bolts didn't fit. The pulley had metric threads. Although not much of a problem as I have a Toolstation nearby I was able to get new bolts quickly. This is the reason I decided to add this post so others could be made aware that some of the new pumps available have metric threaded pulleys. All now back together and running slightly quieter as the bearing in the old pump was worn. The fan had some play in and was slightly loose. I had considered have the original reconditioned but the outlet pipe had quite a bit of corrosion on it and I was concerned that this would not last very long. So something I thought would be a reasonably quick job ended up taking a week. This was just down to waiting for new bolts. Hope this helps others.