This is almost certainly a BOGE strut case as the Koni case used on SWB cars isn't parallel - it has a step change part way down the body,
The BOGE strut body tends to be a 'wet' design with the tube forming the cylinder of the damper.
There is a Bilstein Cartridge insert that fits this strut body (Part No. P36-0111-M512)
These inserts are supplied with a green dust cover.
There used to be two different Bilstein Parts for early SWB strut casings but this changed about 10 years ago when one part was dropped from production.
The problem with fitting these inserts is quite common and due to the poor tolerance of the original BOGE casing.
It is quite common for the new insert not to reach the bottom of the leg and when you tighten up the gland nut there will be some axial float of the insert in the casing - hence the 'clonk' which is only audible at low speed but it there all of the time.
The only way to avoid this problem is to fit shims into the base of the strut casing and ensure that all of the axial clearance has been removed. We have found that shim with a combined thickness of up to 3mm can be needed.
This is not as straightforward as it sounds as the bottom of the strut casing is not flat - it has a small curvature and if a thick plate is fitted it can deform and the problem recurs, this is partly due to the end of the insert being flat and hence mismatched.
It is better to use thin shims say 1mm each, fit them individually and tighten up the gland nut between adding the shims.
Some people fill the casing with oil between the insert and the body and this will help with cooling and will damp out the 'clonk' but it won't stop the movement which will always cause long term damage.
The 'roll pin' used on a Bilstein strut is a bit of a red herring and only relevant to the post 1969 design of strut casing.
