Rear shock absorber bolts

[04-182]

Hi. What size bolts should be in the rear shock absorbers please? Just undone more to change the springs abs shocks but I have different size bolts on each side. One 15mm head and the other 18mm head. The thread on the 15mm one is shot so going to replace both. Does anyone have a link or can tell me which ones I need please?

also. Is there something missing her from under the top mount?

Thanks in advance