On those blades, do you have the original OEM style or have they been replaced as a unit? If original like those on my 69 230/8 and 72 350SL 4.5, then the Bosch rubber blade inserts are available pretty cheap but you need to have the long spring steel inserts that lock them in place. One goes into a groove on each side of each insert to hold it secure, i.e. two per blade. They are simple to remove/replace with needle nose pliers. When you look at an original blade assembly there is no obvious retainer, no claws or hook at one end holding the insert in place. The steel retainers look like part of the blade, but are removable with the needle nose pliers, very simple.

If you have the Anco style replacement inserts with a claw retainer at the end, then you are stuck and need to continue using them unless you can find the OEM steel retainers. The Ancos require you to spreadi the blade slots in the arms slightly so the steel reinforced Anco blade insert will fit and work properly. If you convert back, you'll need to re-tighten the slots in the arms slightly so the insert does not wobble around.

Bosch blade retainers are similar to those used on some of the Japanese cars, like my 2000 Subaru Outback, same style, very simple and effective. A well equiped Indy shop should have the Bosch rubber inserts for around $10 a pair. They are different lengths for DS and PS.

For what its worth...

230/8