The original question said 5-10 kts before V1.
Much comment has ensued, but I guess that what the reverser is doing (or not doing) at that speed could well be totally different 20kts later.
Personally, I would probably reject the take-off, but I've the advantage of having seen inflight reverser deployment many times in the sim.
To say that you would be "mad" to reject is a bit unfair I think .... many factors, in addition to the fault itself, are in play ... for example,for a 733, even at MTOM, a V1 reject at LHR or MUC presents little problem, but would be a different story at LTN.