Hi all, 89 small bumber 8v digi, 170k. When starting up from cold it always runs on 3 cylinders for a few moments then catches on the 4th. Its No1 cylinder thats not firing straight off, I replaced the plugs a couple of months ago which seemed to cure it for a short while, but the problem came back again, I replaced the rotor arm, dizzy cap and leads today but it fired up on three just the same and then settled down just fine. I took the plugs out again and No1 was very dry and tight to get out, the others had slightly oily threads and came out really easily. I've checked the coolant, it seems fine and clean, no mayo in the oil etc. no white smoke, nothing to suggest a HG problem, in fact it ticks over smoothly and runs very well. Just wondering if it could be a sticky injector, if there is such a thing?
Any ideas as to the cause of this problem would be very welcome.

(BTW tried a search but nothing quite like this)