Wildwilliam,
That's actually not a dumb question, because the tank isn't in motion.. I have seen some pics of Panthers without the sag, it just depends on whether the track tensioners have been adjusted.
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As far as aftermarket parts go..
Cromwell models makes two IR sets, both are discontinued.. Here is one part number..
CA18 £5.00 Infra-Red Equipment - kit provides 2 sets.