I had my '69 Corvette Calipers sleeved/rebuilt by LoneStar calipers in 1989, and I rebuilt the MC using std OTS kit, and used DOT 5 in the system at that time, and I haven't had the first issue since. The car only gets driven a few times a year, but No issues with brakes (and THAT is why I used the DOT 5).
The only facts different about your car is that you first used Dot3, then changed to Dot 5 (I think that is generally a No no with rubber seals/parts).
I also had WhitePost rebuild a couple of MC for me over the years ('60 Corvette MC around 1995) and my '69 Z28 MC in 2012; yes WhitePost told me in 2012 not to run Dot 5, but I did it anyway. Without any info/data as to why I don't follow any/all 'suggestions' I get..
Personally I won't worry about it unless I see a leak, and if I do, I'll buy my own seal kit and rebuild again with Dot5.