911S strut assemblies, Inserts don't fit Options

[framos914]

Need help. My 75 2.0 has worn strut inserts, PO replaced front struts with what I believed were 1977 911S Koni struts part #911 341 079 16 stamped on it. Bought inserts Koni 86-1942. Problem is they bottom out before going in far enough to secure them with the round nut.
Could I have 72-74 911S struts? Did they have the same part number? And are those inserts (86-1638) just a little shorter to seat further down. The 1942s seem to be just about 12mm too long, body of the 1942 is 374mm long.

Tried getting info from a few places including Koni but no luck.
Thanks

[sixnotfour]

Question: Some friends told me I ought to put some type of coolant in my strut housing before I install the insert. What are they talking about?

Answer: It's a good idea, particularly if the car is tracked, to put a the strut tube prior to installing the insert. You can use a 50/50 mix of water and antifreeze or hydraulic oil. Many inserts that you remove prior to installing your Koni's, will leave hydraulic oil in the tube. You can use this oil or the antifreeze mix. You'll want the coolant level to be about 2/3 of the way up the insert. It won't take much fluid because the insert will displace most of it. Use the dipstick method to check the level of the fluid. A paper towel can be used to soak up excess if needed. Never run straight water in the tube as if may freeze and collapse your insert.