Well, "maintenance" would mean visual inspection and checking the bearings (basically by wiggling to see if their loose/worn)
Seeing "welding" being mentioned would mean a repair... (rotten cross member?)
The problem I see with a 'simple patch' placed over a damaged area, that this doesn't remove/stop any rust inside... it will continue to decay, now even less visual then before...
Welding seems generally problematical, high chances the heat/cool/contraction starts to warp, twist, misalign something... to avoid that, one must first build a solid rig fixing the to be repaired swing-arm on several critical points... and there is still some risk that the thing might deform during the process...
To me a good, sustained solution seems to acquire a used swing-arm in good condition, add/widen some drainage bores in the relevant cross-member, utilize some top grade cavity protection, and use some proper primer plus protective paint (several thin layers) on the outside (maybe getting it sand-blasted first, but this will dirty-up all cavities, thus make the use/effect of WaxOil or whatever is used more difficult).
Then install new swing-arm bearings, packed with sufficient amounts of marine grease, apply some silicone grease on the V-ring seals, and assemble the whole thing with proper torque on the pivot bolts/lock-nut.