If that trans had 75k on it and you caught the problem early it might be worth the risk to only do the reverse clutches.
The reverse clutches are such a problem that we have often considered doing them with front pump seals. The whole question is made mute when one considers the age. We now very seldom do just front pump seals on cars over 125k. The seals fail at about the same time and doing half the work to replace one seal (or even in this case clutches) is poor economics.
In the case of rear clutch failure, you are going to have a muddy mess for sure in the trans. All that clutch material is in the oil and spread everywhere. It often plugs the filter and is the final straw. If you wait till they are metal to metal the mix is near terminal. Anyone putting just clutches into that mesh is doing you no favor.
We do the 722.3 trannies about 25 a year. A front pump seal/rear main oil seal (you are there why not reseal the motor) would cost about 700 with filter and fluid. Doing rear clutches would add about 200. We disassemble, clean, replace ALL seals (including servo pistons, clutch lip seals, etc), all clutches, thrust bearings, and make all adjustments internally and externally for about 1500.
We hardly ever do less than the 1500 for an old tranny (that needs any of the above) and 180k is an OLD tranny. They call it rebuilding. I call it a 150k tranny service.
The clutches for reverse are MB# 126 272 09 25 and list for $9.25 each and there are 4. They are stacked together with the metal clutches which are likely also bad. They come in various thickness to achieve proper endplay of the stack. The thicknesses are 2.3, 2.8, 3.3, and 3.8mm the smallest cost 36 and the largest costs 19 (figure that).
Bosch Master, ASE Master, L1
33 years MB technician