yeah mate it sounds like the valve seals,
however when it comes to do the seals plug up the rear oil return gallies will a bit of kitchen roll or sumit as this will help prevent the collets dropping into the sump just make sure you dont forget to remove the tissue as you go
oh and use a magnet to get the collets off makes much easier work for you then put a spot of grease /vasaline on the back of them on re-fitting as this stops them from dropping off the valve stem while undoing the valve spring compressor.