ok so i have a d16a6 block and ordered some headstuds,for z6 , because they are the same but problem is on stud is very hard to put in and i think it because the thread on the block is fucked.. if this is true...do i just need to retap the headstud on the block.. and if so what is the size of the tap that i need?

all other studs go in perfect just the one on distrib. side on top left