Clean thoroughly and dismantle conservatively, because a St George wall oven from the 1980s or 1990s predates most parts catalogues and a broken component may be unobtainable. The cavity is plain enamel that takes repeated applications with dwell time.
St George is a genuinely Australian heritage brand, and its wall ovens from the 1980s and 1990s are still working in older Sydney homes across the inner west, the north shore and the southern suburbs.
Forty years of carbon, and forty years of parts history
Two facts about age govern everything here.
The first is that an oven built in 1988 has, if it has been used continuously, been through something on the order of ten thousand heat cycles. What is on the cavity roof is not grease and it is not recent. It behaves like varnish, it responds to contact time and not to force, and it will want three or four applications rather than one. Our oven cleaning guide covers the method.
The second is that the parts catalogue for that appliance largely no longer exists. A door glass panel, an inner trim, a specific shelf runner or a model-specific seal may be genuinely unobtainable, not merely inconvenient.
Dismantle conservatively
That second fact changes the risk calculation rather than the method. On a current oven, taking a door apart to reach between the panes is a reasonable thing to attempt. On a St George it is a decision with a permanent downside, because a cracked panel ends the appliance rather than costing a hundred dollars.
Clean thoroughly, and if a fixing resists, stop rather than persist. This is the brand where that advice matters most.
They were built well
Worth saying, because it explains why so many survive. A St George was a solid appliance with simple electromechanical controls and heavy enamelled cavities, and an owner who keeps one clean and dry can reasonably expect it to keep going.
A St George still working after forty years has earned a careful clean rather than an aggressive one.
The wall oven cabinet around it
A St George wall oven is usually built into joinery that is the same age as the appliance, and on a kitchen of that vintage the two have aged together.
That matters when the oven comes out, which it occasionally must for a proper clean of the sides or to reach a rear panel. Forty year old chipboard cabinetry with forty year old fixings does not always survive being disturbed, and the oven is frequently heavier than the shelf beneath it was ever really rated for.
If the appliance has never been removed, treat that as a job requiring two people and some caution rather than a routine step. It is also worth checking the vent gap above the oven while you are there: on older installations these were sometimes closed up during a later renovation, and an oven venting into a sealed cavity runs hotter than it should and cooks the joinery around it.
What actually goes wrong
A broken part with no replacement, which turns a clean into an appliance decision.
One application and a conclusion, on carbon that needed four.
Abrasives used out of frustration, which dull enamel that has survived four decades.
A perished seal, near certain at this age, and worth checking against what can actually be sourced.
Should you do it yourself?
Do it yourself for the cavity, patiently, without forcing anything.
Get someone in for anything involving dismantling, where the downside is permanent. The St George cooktop is usually the same vintage.