I agree with Tech, replace them with the V70 taillights. THe V70 ones are more durable - also they look a little different. The orange coloured box in the middle on an origiinal 855, is white in a V70's. Orange to white = Not a big deal. Lasts longer = a big deal.
If purchasing a new taillight is not an option at this time, try this:-
1) Clean the taillights well.
2) If you feel taking them off will be easier, then do it.
3) Get the clear (transparent) plastic wrapper-stickers. A good brand is 3M, or any other for that matter.
4) Slowly and carefully paste the clear plastic wrapper onto the cracked taillights.
5) Trim off the excess...
(Seem good to go for another 6 months or so...)