These ar notes I made a few years ago. The 52 will be the same: They may help.

NOTES ON STRIP AND REBUILD OF DIANA 48

Strip:
Remove stock by removing front bolt and the trigger guard bolt / screw (one is a woodscrew). Cross head bolts/screw.

Remove the E clips and pins that secure the sidelever arm and cocking link rod.
Remove sidelever and unscrew the link rod. Note a washer or washers on the sidelever pin .. on our model there is only room for one washer inside the lever housing and we had a second washer under the pin head.

Take the spring pressure either by pushing receiver down on a firm surface or using a compressor. Do not obstruct the safety catch. Spring preload is only moderate. Remove trigger block by pushing out the two pins that go through the action. These pins hold the spring pressure. I pushed them out from the sidelever housing bracket side as I figured it would be easier to refit them from the clear cylinder side.

Let spring expand and remove trigger block .

Spring, spring guide and piston can now be slid out.

To remove piston cylinder, undo the cocking rod bracket bolt (hex head) in the end of the piston cylinder. Remove bolt and pull bracket free. Piston cylinder comes out easily ... it falls over the anti-bear trap mechanism.

If you need to remove anti-bear trap, simply unhook the spring ends, push pivot pin free and remove mechanism.

Breech seal is a hard disc in the piston cylinder end and fits to just below the locating hole for the cocking rod bracket.

Re-assembly:
Basically a reverse of above but note the following.

Refitting trigger block: The pins may not just push through. DO NOT FORCE THEM.
If you look through the holes you will notice a part of the trigger mechanism blocking the hole ... a flat bar / spring. If you hold the block with trigger uppermost, one hole becomes clear as the bar falls out of the way. But it does not always fall completely clear.
To refit, I did:
Secure action in a padded vice, trigger block slot uppermost.
Slide trigger block into the slot against spring pressure and hold in place with a drift. I used a small piece of wood to push the block in so as to not interfere with the safety catch. Look through the free hole. If it is the one with the bar across it then gently move the bar out of the way (downwards) with a small screwdriver. When hole is clear, push the pin through. Remove the drift from other hole. Looking through the hole, notice a curved end to a sprung bar. Lift safety catch up and note how the bar moves to give room for the second pin to go in. Replace second pin while holding safety catch up.

When this is done, refit the underlever cocking rod and sidelever. The breech seal contact is adjustable: With the piston cylinder against the breech seal, the sidelever end should rest about 2 inches from the action and just need a gentle push to go ‘over centre’ and rest against the action. If this is not so, remove the cocking rod link pin and adjust length of the rod using the adjuster nut on the rod near the pin. Replace pin.

Cheers, Phil