I have a 99 Civic with an oil pan leak, rear main seal leak, and leak inside the timing belt cover.

Assuming I can keep the oil topped off... what damage do I risk if I don't get these repairs done?

 

The leak inside the timing cover will saturate the timing belt. Long term exposure will damage the belt and a timing failure will occur. If the vehicle has a manual transmission, the rear main seal leak will saturate the clutch disc... this will cause the clutch to eventually slip.

 

timing cover= fix the leak, been there done that, if you dont fix it, then you get to buy another head,
the belt WILL snap and take out the valves, when that happens, you get to call your boss and explain why your going to be late
Are you sure its the rear main seal? Reason I ask is oil can move in wierd ways, It may be just the oil pan gasket. Drop the exhaust at the head, let the exhaust hang and drop the pan. fix the leak.
One spot you didnt mention is the oil pressure sender. When that starts leaking, it makes a heck of a mess. If its a D15 engine there is a oil catch can under the intake manifold, when those o ring and hoses go bad it REALLY make a mess
If you dont fix all the leaks, at least fix the timing cover
Good luck

 

It can be tough stopping these engines from leaking. I swear it seems the oil pan is happier when it's leaking. Not saying I'm happier, but the pan sure seems to be. I agree with the rest of the posters that you should definitely deal with the front crank and or or cam seal if it's leaking.

 

Where is the oil pressure sending unit on the D15?

 

Back of the block near the alternator for the light on the dash... I think the reference above would be for the VTEC oil pressure switch, and that sensor is found on the VTEC assembly which is bolted to the rear right hand corner of the cylinder head.

 

D15 looking at the engine from above, under the intake on the right side just below the head. you access it from underneath the car. DO NOT OVER TIGHTEN