I have more or less the same problem except that bolts go straight up into the headstock casting and they ooze a very small amount of the gear oil. To put it into perspective, I filled the headstock to to its max oil level in about 1983 and re-filled it because in 2013, because I moved house and I wanted a fresh start. So less then .5l lost in that time! Interestingly the oil had gone black – bacterial degradation?
I think the technique is to lift the lathe slightly of its stand and block up under the bed or on any suitable surface with the bolts just undone by 3mm or so. Then if using silicone which I would think would work, de-oil the surfaces thoroughly and give the top of the stand a good bead near its outside edge. Leave it for 15 min to skin over, remove the blocking gently and tighten up the bolts.
If this is not possible, then a good cleaning to de-suds the area and just put a fillet on the outside should work.
FWIW I use to fix rockerbox and sump gaskets with silicone goo, good for engine oil up to 90 degs C! But the surfaces were clamped.
Frank