The ones on my turbo were siezed too,

I tried with WD40, left it on for a week, but it did nothing
The last resort was heating it up with a blow torch.(turbo on workbench-vice )

Be carefull of the ones on the turbine intake, they need heating from the inside for best results as they are surrounded by too much metal and heat dissipates quickly (as its supposed to)


EDIT:P.S. If the bolts are seized, the core will probably be siezed to the housing too. I held the housing on the vice, and tapped the core with a hammer gently and evenly all around (paralel to the turbo shaft, hammering onto an extension bit - not directly)




Dont forget that hot things can burn your hands (and whatever you do, do not -I repeat - DO NOT pick up the bolts of the floor like I did)