1983 gsl 12A stock. I've been checking my oil level - for the past few weeks they have been full or maybe alittle over full. Yesterday after sitting in a level space for over 8 hrs. I checked it and the oil mark was between the low mark and the end of the stick! Wiped and rechecked it showed full? rechecked again it showed full. In the last week or so my oil pressure has been a little lower at speed. any ideas would be greatly appreciated. thanks