Further on this topic, I bought from eBay a cheap temperature-controlled hot air desoldering gun (like this one) on the basis that even if it wouldn't cure a bodged chassis it would certainly be useful for bodged PCBs, of which I have a growing number.
Its first use was to unsolder a whitemetal chimney. It had been crookedly but very thoroughly attached using 100 degree solder onto a pre-tinned smokebox, so I did not hold much hope of getting it off unscathed. But after a few minutes of hot air, starting gingerly at 120 degrees and increasing to 160 (to overcome the heatsink effect), it popped off undamaged.
No doubt I will soon give myself the opportunity to discover if it will deal as efficiently with 145 degree and electrical solder.