M6X1 20mm torqued to 10 NM
I think the original cap heads are 20mm long, but both sides will take a 25mm long screw.
If the screw has broken inside the reservoir housing you have a delicate surgery task in front of you, easy-out, or maybe even very small drill then easy-out.
Hopefully there is a wee bit of the screw protruding from the reservoir housing and you can grab it with a set of multi-grips.
I think the original cap heads are 20mm long, but both sides will take a 25mm long screw.
If the screw has broken inside the reservoir housing you have a delicate surgery task in front of you, easy-out, or maybe even very small drill then easy-out.
Hopefully there is a wee bit of the screw protruding from the reservoir housing and you can grab it with a set of multi-grips.