Oh dear, poor thing! Has it had plenty of water and lots of good manure or compost - they are greedy feeders.

It could be too much or too little water! Im a very new gardner so can only tell you about the conditions in my rhubarb patch and what I've found out on doing some Google research. My patch was once granny-in-law's and the rhubarb has been growing well there for years! Rhubarb needs damp but well drained soil and doesn't like hot weather. Your red spots sound like a fungus. If it was my rhubarb, I would remove all the stalks that have leaves with red spots to try and get rid of the fungus. I have sandy soil already but you might benefit from adding some sand to the soil in your rhubarb patch if the water doesn't drain away easily. Failing that, your yellow wilted leaves may be a result of root rot and unfortunately I haven't found anything that can solve that problem apart from digging it up and starting again :( Also make sure your rhubarb has plenty of room. Someone told me it needs at least 3 feet on all sides! Not sure if they were having me on though!

No they weren't Mizzie! Planting nearer won't hurt the rhubarb but the leaves will bend over and cover up whatever you've planted there. Very unlikely to be too much water I would think, unless the ground is actually boggy.Almost any soil will do so I wouldn't bother adding sand - better use compost or well rotted manure if the soil needs improving - in fact do it anyway. I'd guess the problems due to impoverished soil - do other things grow well nearby?
Maggie if you are going to stay with Goy it helps to put your county on your profile to give us an idea of your climatic conditions.

Hi, welcome to GoY, the brown spots on the leaves could be Ramularia and Ascochyta, {fungi}, which overwinters in infected plant debris, don't overwater, try to water the soil instead of the leaves, and water early in the day, so it can dry out.
The leaves turning yellow coul be caused by root an crown rot, have a look at the crowns for evidence of a brown - black decay, examine the large roots to see if there are any small feeder roots, if they're lacking, it coul be evidence of crown and root rot, and larger roots could have brown - black holes in them, if this is the case, I would discard the plants, and not grow rhubarb in the same position for a few years, Derek