better make that three recommendations to straighten the bath!!
sounds like your making life unecessarily complex by not having a level bath top (as the bath was designed to be fitted this way anyway!!)
My Baxi Solo 2 boiler started leaking water everywhere the other day.
i took the front cover and inner cover off and was confronted with some serious corosion all along the bottom row of plates on the heat exchanger. :(
In my head, i've written the boiler off as it's about 15 years old, but...