808 diff schim?

Hi, dont know if i spelled it correct but should i shim My diffs? I have taken it apart to clean it and noticed that the front pinion can be pulled 1-2mm front to back and the back 2mm or so. I bought it last summer used and drove it at the track à few times, no problem, no signs of wear what so ever but wondering if I should shims the diff and what size if thats the case. Running tekin 1700 truggy combo with 5s. Thanks