I've already been through this stuff about 10 years ago concerning the engine oil.
If you move directly to fully synth your going to get a load of
'GUNK' washed out from your engine/block.
If your gaskets 'fail' it's because they were all already
'GUNKED UP' with all of the
'GUNK' from the old engine oil
All the '90/'91 etc Turbo cars in the USA are running full synth oil. It's what I switched to years ago and it's easier for the oil pump to pump it - slightly less oil pressure needed to supply the engine/block even when Turbo'd as the engine is not
'GUNKED UP' with all of that black stuff anymore
It washes out ALL of the old engine oil
'GUNK' when you switch over (therefore go to half-synth first or you'll find all of your
bad gaskets all at the same time). The engine gets up to temp faster, it cools quicker, it runs free'er and it no longer has any of that old
'BLACK GUNK' in it.
What do you want ? A better performing engine/block or to just hold on to your bad gunk'ed up gaskets in a gunk'ed up engine/block ?
Yes, you will need to do more oil/filter changes at first because your washing all of that
'BLACK GUNK' out of it, but when it's done it's done.