Inspect the thread on the bolts, the thread damaged one in the pic I had to tidy it up with a little jewellers file. I've also had some that are not entirely straight. If a bolt struggles to go in.... try another bolt to determine if it's the bolt or the hole with the problem.
Make sure the bolt holes are spotless, I use brake cleaner, a wire twist drill bit, compressed air and then make sure every bolt can be hand inserted to it's stop point freely before installing the component. You can also cut a slot with a grinder into the old bolts and use them as a thread cleaner in the bolt holes.

 

Inspect the thread on the bolts, the thread damaged one in the pic I had to tidy it up with a little jewellers file. I've also had some that are not entirely straight. If a bolt struggles to go in.... try another bolt to determine if it's the bolt or the hole with the problem.
Make sure the bolt holes are spotless, I use brake cleaner, a wire twist drill bit, compressed air and then make sure every bolt can be hand inserted to it's stop point freely before installing the component. You can also cut a slot with a grinder into the old bolts and use them as a thread cleaner in the bolt holes.

View attachment 22952

View attachment 22953

Thanks for all of this, it was actually a bit simpler, vendor sold me the wrong bolts, took a little while to notice but got there in the end!
Thanks