Cant remember who it was who was having starter problems like me recently. I took downpipe off (bugger to reseal) got to starter and found the spade connector slightly corroded. Didnt believe it was only that, but didnt have a new starter so cleaned it, and reassembled (thin hands helps). Since then the starter is definetly better, everytime and spinning faster than I ever remember it (was always lazy before it stopped altogether).
Seems to be a trap fro loads of crap falling downback of block, which makes it mangy and prone to rust. Try this before shelling out 100 odd squid on new starter, mines got 78k, how long 16v starters last, this might be common!